Edgar Filing: XOMA Corp

form424b5.htm

Filed Pursuant to

Rule 424(b)(5)

Registration No.

333-183486

PRELIMINARY PROSPECTUS SUPPLEMENT TO PROSPECTUS DATED SEPTEMBER 7, 2012

13,333,333 Shares

Common Stock

We are offering 13,333,333 shares of our common stock.

Our common stock is listed on The NASDAQ Global Market under the symbol “XOMA.” The last reported sale price of our common stock on The NASDAQ Global Market on October 23, 2012, was $3.22 per share.

The underwriters have an option to purchase a maximum of 1,999,999 additional shares of our common stock.

Investing in our common stock involves a high degree of risk. See the risks set forth under the heading “Risk Factors” beginning on page S-6.

	Price to Public		Underwriting Discounts and Commissions		Proceeds to Us
Per Share	$	3.00	$	0.18	$	2.82
Total	$	39,999,999	$	2,400,000	$	37,599,999

Delivery of the shares of common stock is expected to be made on or about October 29, 2012.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Credit Suisse

Cowen and Company

The date of this prospectus supplement is October 24, 2012.

TABLE OF CONTENTS

Prospectus Supplement		Prospectus

ABOUT THIS PROSPECTUS SUPPLEMENT	S-ii	ABOUT THIS PROSPECTUS	i
PROSPECTUS SUPPLEMENT SUMMARY	S-1	PROSPECTUS SUMMARY	1
RISK FACTORS	S-6	RISK FACTORS	5
FORWARD-LOOKING INFORMATION	S-29	SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	5
USE OF PROCEEDS	S-30	USE OF PROCEEDS	7
DILUTION	S-30	RATIO OF EARNINGS TO FIXED CHARGES	7
UNDERWRITING	S-31	DESCRIPTION OF CAPITAL STOCK	7
NOTICE TO CANADIAN RESIDENTS	S-34	DESCRIPTION OF DEBT SECURITIES	12
LEGAL MATTERS	S-35	DESCRIPTION OF WARRANTS	18
EXPERTS	S-36	LEGAL OWNERSHIP OF SECURITIES	20
WHERE YOU CAN FIND MORE INFORMATION	S-36	PLAN OF DISTRIBUTION	23
INCORPORATION OF DOCUMENTS BY REFERENCE	S-36	LEGAL MATTERS	24
		EXPERTS	24
		WHERE YOU CAN FIND MORE INFORMATION	24
		INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	25

You should rely only on the information incorporated by reference or provided in this prospectus supplement, the accompanying prospectus and any free writing prospectus that we have authorized for use in connection with this offering. Neither we nor the underwriters have authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell, or a solicitation of an offer to purchase, the securities offered by this prospectus supplement and the accompanying prospectus in any jurisdiction where it is unlawful to make such offer or solicitation. You should assume that the information contained in this prospectus supplement or the accompanying prospectus, or any document incorporated by reference in this prospectus supplement or the accompanying prospectus, and any free writing prospectus that we have authorized for use in connection with this offering is accurate only as of the date of those respective documents. Neither the delivery of this prospectus supplement nor any distribution of securities pursuant to this prospectus supplement shall, under any circumstances, create any implication that there has been no change in the information set forth or incorporated by reference into this prospectus supplement or in our affairs since the date of this prospectus supplement. Our business, financial condition, results of operations and prospects may have changed since that date.

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ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement is part of a registration statement (No. 333-183486) that we filed with the Securities and Exchange Commission (the “SEC”) using a “shelf” registration process. Under the registration statement, we registered the offering by us of common stock, preferred stock, debt securities and warrants for sale from time to time in one or more offerings. This prospectus supplement provides specific information about the offering by us of our common stock under the shelf registration statement. This document is in two parts. The first part is the prospectus supplement, which adds to and updates information contained in the accompanying prospectus. The second part, the prospectus, provides more general information, some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus, on the other hand, you should rely on the information in this prospectus supplement.

Before purchasing any securities, you should carefully read both this prospectus supplement and the accompanying prospectus, together with the documents incorporated by reference herein as described under the heading “Incorporation of Documents By Reference” and the additional information described under the heading, “Where You Can Find More Information” in this prospectus supplement, as well as any free writing prospectus prepared by or on behalf of us or to which we have referred you.

Unless the context otherwise requires, references in this prospectus supplement to “we”, “us” and “our” refer to XOMA Corporation and its consolidated subsidiaries.

This prospectus supplement and the accompanying prospectus, including the information incorporated by reference into this prospectus supplement and the accompanying prospectus, include trademarks, service marks and trade names owned by us or others. XOMA, the XOMA logo and all other XOMA product and service names are registered or unregistered trademarks of XOMA Corporation or a subsidiary of XOMA Corporation in the United States and in other selected countries. EYEGUARD is a service mark of a subsidiary of XOMA Corporation in the United States. All other trademarks, service marks and trade names included or incorporated by reference in this prospectus supplement and the accompanying prospectus are the property of their respective owners.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information about our company, this offering and information appearing elsewhere in this prospectus supplement, in the accompanying prospectus, in the documents we incorporate by reference and in any free writing prospectus that we have authorized for use in connection with this offering. This summary is not complete and does not contain all the information that you should consider before investing in our common stock. You should read this entire prospectus supplement and the accompanying prospectus carefully, including the “Risk Factors” contained in this prospectus supplement, the accompanying prospectus and the financial documents and notes incorporated by reference in this prospectus supplement and the accompanying prospectus and any free writing prospectus that we have authorized for use in connection with this offering, before making an investment decision. This prospectus supplement may add to, update or change information in the accompanying prospectus.

Overview

XOMA Corporation (“XOMA”), a Delaware corporation, discovers and develops innovative antibody-based therapeutics. Our lead drug candidate is gevokizumab (formerly XOMA 052), a humanized monoclonal allosteric modulating antibody that binds to the inflammatory cytokine interleukin-1 beta (“IL-1 beta”). In collaboration with our partner, Les Laboratoires Servier (“Servier”), we have initiated three Phase 3 clinical trials evaluating gevokizumab for the treatment of non-infectious uveitis (“NIU”) and Behçet’s uveitis, and we are screening and enrolling patients in these three separate studies. XOMA is conducting two of these studies, both in NIU, and Servier is conducting the Phase 3 study in Behçet’s uveitis. We anticipate Servier also will enter gevokizumab into a Phase 2 study in a cardiovascular disease indication during 2012. Separately, we have launched a Phase 2 proof-of-concept program for gevokizumab to evaluate additional indications for further development, including a clinical trial in moderate-to-severe inflammatory acne, which began enrolling patients in December 2011, and a clinical trial in erosive osteoarthritis of the hand, which was opened for enrollment in June 2012. We anticipate initiating a proof-of-concept study of gevokizumab in a third indication in the fourth quarter of 2012.

We have entered into a license and collaboration agreement with Servier to jointly develop and commercialize gevokizumab in multiple indications. Gevokizumab is designed to inhibit the pro-inflammatory cytokine IL-1 beta, which is believed to be a primary trigger of pathologic inflammation in multiple diseases. Under the terms of the agreement, Servier has worldwide rights to gevokizumab for cardiovascular disease and diabetes indications and rights outside the United States and Japan to all other indications. We retain development and commercialization rights in the United States and Japan to all indications except cardiovascular disease and diabetes and have an option to reacquire rights to these indications from Servier in these territories. Should we exercise our option to reacquire rights to the cardiovascular disease and diabetes indications in the United States and Japan, we will be required to pay Servier an option fee and reimburse a specific percentage of Servier’s incurred development expenses.

Our proprietary preclinical pipeline includes classes of antibodies that activate or sensitize the insulin receptor in vivo, named XMet, and represent potential new therapeutic approaches to the treatment of diabetes and several diseases that have insulin involvement and that we believe may be orphan drug opportunities. We have developed these and other antibodies using some or all of our ADAPT™ antibody discovery and development platform, our ModulX™ technologies for generating allosterically modulating antibodies, and our OptimX™ technologies for optimizing biophysical properties of antibodies, including affinity, immunogenicity, stability and manufacturability.

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XOMA 3AB, a biodefense anti-botulism product candidate comprising a combination of antibodies, was developed through funding from the National Institute of Allergy and Infectious Diseases (“NIAID”) of the U.S. National Institutes of Health (“NIH”). Enrollment and dosing of all cohorts has been completed in a Phase 1 clinical trial sponsored by NIAID. In January 2012, we announced we will complete NIAID biodefense contracts currently in place but will not actively pursue future contracts. Should the government choose to acquire XOMA 3AB or other biodefense products in the future, we expect to be able to provide these antibodies through an outside manufacturer.

We also have developed antibody product candidates with premier pharmaceutical companies including an affiliate of Novartis AG (“Novartis”) and Takeda Pharmaceutical Company Limited (“Takeda”). Two antibodies developed with Novartis, LFA102 and HCD122 (lucatumumab), are in Phase 1 and/or 2 clinical development by Novartis for the potential treatment of breast or prostate cancer and hematological malignancies, respectively.

In January 2012, we announced we had acquired U.S. rights to the perindopril franchise from Servier. The agreement includes ACEON® (perindopril erbumine), a currently marketed angiotensin converting enzyme (“ACE”) inhibitor monotherapy, and an additional fixed-dose combination (“FDC”) product candidate in which perindopril is combined with another active ingredient(s), such as a calcium channel blocker. The longest of the patents relating to the proprietary form of perindopril in combination product candidates expires in April 2023. We assumed commercialization activities for ACEON® in January 2012 following the transfer from Servier and its previous U.S. licensee. In February 2012, we initiated enrollment in a Phase 3 trial for the fixed-dose combination product candidate from the perindopril franchise, which combines perindopril arginine and amlodipine besylate (“FDC1”). The trial, named PATH (Perindopril Amlodipine for the Treatment of Hypertension), is expected to enroll approximately 816 patients with hypertension to determine the safety and efficacy of the fixed-dose combination versus either perindopril or amlodipine alone. The primary and secondary endpoints are reduction in sitting diastolic and systolic blood pressure, respectively, from baseline after six weeks of treatment. Based on regulatory interaction to date, if positive, we expect this trial to be the only additional efficacy trial needed to complement the existing body of clinical data to support the submission of a New Drug Application to the Food and Drug Administration (“FDA”) seeking marketing approval for this product candidate. Servier provided partial funding for the PATH trial; the balance of study expenses, consisting primarily of costs generated by our contract research organization, are expected to be paid by us over time from any profits generated by our ACEON® sales.

In January 2012, we implemented a streamlining and restructuring designed to sharpen our focus on value-creating opportunities, led by gevokizumab and our antibody discovery and development capabilities. The restructuring plan included a personnel reduction of 84 positions, or 34% of our staff. These staff reductions resulted primarily from our decisions to utilize a contract manufacturing organization for Phase 3 and commercial antibody production and to eliminate internal research functions that are non-differentiating or that can be obtained cost-effectively by contract service providers. In August 2012, we and Servier announced we had entered into an agreement with Boehringer Ingelheim to transfer XOMA's technology and processes for the validation of our technology and processes in preparation for the commercial manufacture of gevokizumab. Upon the successful completion of the transfer and the establishment of biological comparability, including validation of the XOMA processes, it is our intention that Boehringer Ingelheim will produce gevokizumab for XOMA's commercial use at its facility in Biberach, Germany.

Product Development Strategy

We are advancing a pipeline of antibody product candidates using our proven expertise, technologies and capabilities from antibody discovery through product development. We seek to expand our pipeline by developing additional proprietary products and technologies and by entering into additional licensing and collaborative arrangements with pharmaceutical and biotechnology companies. The principal elements of our strategy are to:

Focus on advancing gevokizumab, our lead product candidate. Using our proprietary antibody technologies, capabilities and expertise, we discovered gevokizumab, an antibody that inhibits IL-1 beta, a cytokine that triggers inflammatory pathways in the body. We believe gevokizumab, by targeting IL-1 beta, has the potential to address the underlying inflammatory causes of a wide range of unmet medical needs.

In December 2010, we entered into an agreement with Servier to jointly develop and commercialize gevokizumab in multiple indications, which provided for a non-refundable upfront payment of $15.0 million that we received in January 2011. In connection with this agreement, Servier is funding the first $50.0 million of gevokizumab global clinical development and chemistry and manufacturing controls (“CMC”) expenses and 50% of further expenses for the Behçet’s uveitis and NIU indications. This funding by Servier under the collaboration agreement includes the NIU Phase 3 trials discussed below.

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In March 2011, we announced our Phase 2b trial of gevokizumab in 421 Type 2 diabetes patients did not achieve the primary endpoint of reduction in hemoglobin A1c (“HbA1c”) after six monthly treatments with gevokizumab compared to placebo. However, significant decreases in C-reactive protein (“CRP”), a biomarker for inflammatory diseases and the risk of heart attack, stroke and other cardiovascular diseases, were observed in all dose groups versus placebo. Results from a Phase 2a gevokizumab trial in 74 patients with Type 2 diabetes, announced in June 2011, were consistent with the Phase 2b results. Gevokizumab was well tolerated in these trials, with no significant differences in adverse events between gevokizumab and placebo, and no serious drug-related adverse events were observed.

Servier and we have initiated an expanded gevokizumab clinical development plan. The plan includes two global Phase 3 trials in active and controlled NIU involving the intermediate and/or posterior segments of the eye, and a Phase 3 trial outside the U.S. in a subset of NIU patients who suffer from Behçet’s uveitis. All three Phase 3 trials have been initiated: the first NIU trial in June 2012, named EYEGUARD™-A; the Behçet’s uveitis trial in September 2012, named EYEGUARD™-B; and the second NIU trial in October 2012, named EYEGUARD™-C. In addition to establishing efficacy, these trials have been designed to meet the FDA safety requirement for ophthalmic indications: at least 300 patients must be treated for at least six months and 100 patients for one year at the to-be-marketed dose. We anticipate we will have preliminary top-line results from EYEGUARD™-A by year-end 2013; EYEGUARD™-B during the first half of 2014; and EYEGUARD™-C during the first quarter of 2014.

We also announced a Phase 2 proof-of-concept clinical program to identify additional conditions that may respond to treatment with gevokizumab. The program is evaluating gevokizumab in three separate diseases that have demonstrated IL-1 beta involvement. The first study in moderate to severe inflammatory acne began enrolling patients in December 2011. In June 2012, we announced the second clinical study in this program, which will study gevokizumab in patients with erosive osteoarthritis of the hand, was opened for enrollment. Later in 2012, we plan to announce the final proof-of-concept indication. Based upon our discussions, we believe Servier intends to advance gevokizumab into Phase 2 development for cardiovascular disease in late 2012. We anticipate we will have preliminary top-line results from the acne trial at approximately year-end 2012; the erosive osteoarthritis of the hand trial in mid-2013; and the final proof-of-concept trial by mid- to late-2013.

In addition, in 2013 we plan to initiate additional Phase 3 clinical studies in two additional indications – Schnitzler syndrome and Neutrophilic Dermatoses – which we believe are ultra-rare diseases (which we consider to be diseases affecting less than one in 50,000 persons). We intend to pursue orphan drug designations for these indications and believe that these two disease opportunities represent attractive markets because they may be eligible for accelerated approval pathways with the FDA, increasing the potential for shorter development timelines and faster paths to commercialization.

Advance our proprietary preclinical pipeline candidates and generate revenues from our proprietary technologies. We will continue to develop our proprietary preclinical pipeline, primarily focusing on the development of allosteric modulating monoclonal antibodies. Our most advanced program, which targets the insulin receptor, has generated three new classes of fully human monoclonal antibodies. These allosteric modulating antibodies activate (XMetA) or sensitize (XMetS) or antagonize/deactivate (XMetD) the insulin receptor in vivo. XMetA and XMetS represent the potential for distinct, new therapeutic approaches for the treatment of patients with diabetes. Separate studies of XMetA and XMetS have demonstrated reduced fasting blood glucose levels and improved glucose tolerance in mouse models of diabetes. We expect to seek a collaborative partner for each of XMetA and XMetS development and commercialization at a future date. In the case of XMetD, we plan to develop this compound internally, as it has potential as a treatment for as many as three ultra-rare life-threatening or severely debilitating diseases: Insulinomas, Congenital hyperinsulinism and Hyperinsulinemic hypoglycemia in post-gastric bypass surgery patients.

Historically, we have established technology collaborations with several companies to provide access to multiple XOMA proprietary antibody discovery and optimization technologies. In addition, we licensed our bacterial cell expression (“BCE”) technology to more than 60 companies in exchange for license, milestone and other fees, royalties and complementary technologies; a number of licensed product candidates are in clinical development. We believe we can continue to generate licensing revenue from our proprietary technologies in the future.

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Complete current biodefense contracts. To date, we have been awarded four contracts, totaling approximately $120 million, from NIAID to support development of XOMA 3AB and several product candidates for the treatment of botulism poisoning. In addition, our biodefense programs included two subcontracts from SRI International totaling $4.3 million, funded through NIAID, for the development of antibodies to neutralize H1N1 and H5N1 influenza viruses and the virus that causes severe acute respiratory syndrome (“SARS”).

NIAID is conducting a Phase 1 trial of XOMA 3AB, a novel formulation of three antibodies designed to prevent and treat botulism poisoning. This double-blind, dose-escalation study in approximately 24 healthy volunteers is designed to assess the safety and tolerability and determine the pharmacokinetic profile of XOMA 3AB. All volunteers in this trial have been enrolled and dosed with XOMA 3AB.

In January 2012, we announced we will complete NIAID biodefense contracts currently in place but will not actively pursue future contracts. Should the government choose to acquire XOMA 3AB or other biodefense products in the future, we expect to be able to provide these antibodies through an outside manufacturer.

Commercialization Strategy

We are committed to establishing XOMA as a commercial organization in the U.S. to capture appropriate value from our product discovery and development programs. In January 2012, we announced we had acquired U.S. rights, and we assumed commercialization activities, for the branded antihypertensive product ACEON® (perindopril erbumine), an FDA-approved ACE inhibitor, from Servier and its previous U.S. licensee. In addition to ACEON®, upon exercise by us of an option with respect to each product, the acquisition includes a portfolio of additional fixed-dose combination product candidates where perindopril is combined with another active ingredient(s), such as a calcium channel blocker.

ACEON® is subject to competition from multiple approved generic perindopril erbumine products, and our commercialization activities are limited to distribution and post marketing regulatory responsibilities as the current holder of the ACEON® New Drug Application (“NDA”). We have contracted with third parties to manufacture and distribute ACEON®.

Financial Update

As of September 30, 2012, our cash, cash equivalents and short-term investments were $59.2 million.

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THE OFFERING

Common stock we are offering	13,333,333 shares (or 15,333,332 shares if the underwriters exercise their over-allotment option in full)

Common stock to be issued and outstanding after the offering	81,440,449 shares(1) (or 83,440,448 shares if the underwriters exercise their over-allotment option in full)

Listing	Our common stock is listed on The NASDAQ Global Market under the symbol “XOMA.”

Use of proceeds	We currently intend to use the net proceeds from this offering for continued development, preclinical testing and clinical studies related to gevokizumab and our XMet platform. We intend to use the remainder of the net proceeds for general research and development, business development and other corporate purposes as determined by our management. See “Use of Proceeds” below.

Risk factors	You should carefully consider the information in “Risk Factors” beginning on page S-6 of this prospectus supplement for a discussion of factors you should consider carefully when making a decision to invest in our common stock.

(1) The number of shares of our common stock that will be issued and outstanding immediately after this offering as shown above is based on 68,107,116 shares of common stock issued and outstanding as of June 30, 2012, and excludes the following:

shares of common stock issuable upon the exercise of stock options outstanding, of which there were 5,709,599 outstanding as of June 30, 2012, with a weighted average exercise price of $10.18 per share;

shares of common stock issuable upon the vesting of outstanding restricted stock units, of which there were 1,387,048 outstanding as of June 30, 2012;

shares of common stock issuable upon the exercise of our outstanding warrants, of which there were warrants outstanding as of June 30, 2012, to purchase 347,826 shares of common stock at an exercise price of $19.50 per share, 1,260,000 shares of common stock at an exercise price of $10.50 per share, 14,829,167 shares of common stock at an exercise price of $1.76 per share, and 263,158 shares of common stock at an exercise price of $1.14 per share; and

7,930,944 shares of common stock not subject to stock awards and reserved for issuance under our equity incentive plans and 91,546 shares of common stock reserved for issuance under our employee stock purchase plan.

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RISK FACTORS

Any investment in our securities involves a high degree of risk, including the risks described below. Before purchasing our common stock, you should carefully consider the risk factors set forth below, as well as all other information contained in this prospectus supplement and the accompanying prospectus and incorporated by reference, including our consolidated financial statements and the related notes and the additional risk factors contained in our most recent Annual Report on Form 10-K and Quarterly Reports on Form 10-Q, as well as any amendments thereto, as filed with the SEC, and any free writing prospectus that we have authorized for use in connection with this offering, before deciding whether to invest in our common stock. The risks and uncertainties described below are not the only risks and uncertainties we face. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also impair our business operations. If any of the following risks actually occur, our business, financial condition and results of operations could suffer. As a result, the trading price of our stock could decline, perhaps significantly, and you could lose all or part of your investment. The risks discussed below also include forward-looking statements and our actual results may differ substantially from those discussed in these forward-looking statements. See the section entitled “Forward-Looking Information.”

Risks Relating to Our Business

Because our product candidates are still being developed, we will require substantial funds to continue; we cannot be certain that funds will be available and, if they are not available, we may have to take actions that could adversely affect your investment and may not be able to continue operations.

We will need to commit substantial funds to continue development of our product candidates and we may not be able to obtain sufficient funds on acceptable terms, or at all. If we raise additional funds by issuing equity securities, including by the sale of common stock in this offering, our stockholders will experience dilution. Any debt financing or additional equity that we raise may contain terms that are not favorable to our stockholders or us. If we raise additional funds through collaboration and licensing arrangements with third parties, we may be required to relinquish some rights to our technologies or our product candidates, grant licenses on terms that are not favorable to us or enter into a collaboration arrangement for a product candidate at an earlier stage of development or for a lesser amount than we might otherwise choose.

Additional funds may not be available when we need them on terms that are acceptable to us, or at all. If adequate funds are not available on a timely basis, we may:

terminate or delay clinical trials for one or more of our product candidates;

further reduce our headcount and capital or operating expenditures; or

curtail our spending on protecting our intellectual property.

We finance our operations primarily through our multiple revenue streams resulting from discovery and development collaborations, biodefense contracts, the licensing of our antibody technologies, and sales of our common stock. In September 2009, we sold our royalty interest in LUCENTIS® to Genentech, Inc., a wholly-owned member of the Roche Group (“Genentech”) for gross proceeds of $25.0 million, including royalty revenue from the second quarter of 2009. These proceeds, along with other funds, were used to fully repay our loan from Goldman Sachs Specialty Lending Holdings, Inc. (“Goldman Sachs”). As a result, we no longer have a royalty interest in LUCENTIS. In August 2010, we sold our royalty interest in CIMZIA® for gross proceeds of $4.0 million, including royalty revenue from the second quarter of 2010. As a result, we no longer have a royalty interest in CIMZIA. We received revenue from this royalty interest of $0.5 million in 2010 and $0.5 million in 2009.

Based on our cash, cash equivalents and short-term investments of $59.2 million at September 30, 2012, anticipated spending levels, anticipated cash inflows from collaborations, biodefense contracts and licensing transactions, funding availability including under our loan agreements, and the proceeds from this offering, we believe we have sufficient cash resources to meet our anticipated net cash needs into the fourth quarter of 2014. Any significant revenue shortfalls, increases in planned spending on development programs or more rapid progress of development programs than anticipated, as well as the unavailability of anticipated sources of funding, could shorten this period or otherwise have a material adverse impact on our ability to finance our continued operations. If adequate funds are not available, we will be required to delay, reduce the scope of, or eliminate one or more of our product development programs and further reduce personnel-related costs. Progress or setbacks by potentially competing products may also affect our ability to raise new funding on acceptable terms. As a result, we do not know when or whether:

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operations will generate meaningful funds;

additional agreements for product development funding can be reached;

strategic alliances can be negotiated; or

adequate additional financing will be available for us to finance our own development on acceptable terms, or at all.

Because all of our product candidates are still being developed, we have sustained losses in the past and we expect to sustain losses in the future.

We have experienced significant losses and, as of June 30, 2012, we had an accumulated deficit of $932.6 million.

For the three and six months ended June 30, 2012, we had net losses of approximately $16.2 million or $0.24 per share of common stock (basic and diluted) and $46.6 million or $0.83 per share of common stock (basic and diluted), respectively. For the three and six months ended June 30, 2011, we had net losses of approximately $8.1 million or $0.27 per share of common stock (basic and diluted) and $14.5 million or $0.49 per share of common stock (basic and diluted), respectively.

Our ability to achieve profitability is dependent in large part on the success of our development programs, obtaining regulatory approval for our product candidates and licensing certain of our preclinical compounds, all of which are uncertain. Our ability to fund our ongoing operations is dependent on the foregoing factors and on our ability to secure additional funds. Because our product candidates are still being developed, we do not know whether we will ever achieve sustained profitability or whether cash flow from future operations will be sufficient to meet our needs.

We are substantially dependent on Servier for the development and commercialization of gevokizumab and for other aspects of our business, and if we are unable to maintain our relationship with Servier, or Servier does not perform under our agreements with Servier, our business would be significantly harmed.

We have a number of agreements with Servier which are material to the conduct of our business, including:

In December 2010, we entered into a license and collaboration agreement with Servier, to jointly develop and commercialize gevokizumab in multiple indications. Under the terms of the agreement, Servier has worldwide rights to diabetes and cardiovascular disease indications and rights outside the United States and Japan to all other indications, including Behçet’s uveitis and other inflammatory and oncology indications. In late 2011, we announced that Servier agreed to include the NIU Phase 3 trials under the terms of the collaboration agreement for Behçet’s uveitis. We retain development and commercialization rights for NIU and other inflammatory disease and oncology indications in the United States and Japan and have an option to reacquire rights to diabetes and cardiovascular disease indications from Servier in these territories. Should we exercise this option, we will be required to pay Servier an option fee and partially reimburse a specified portion of Servier’s incurred development expenses. The agreement contains mutual customary termination rights relating to matters such as material breach by either party. Servier may terminate for safety issues and we may terminate the agreement, with respect to a particular country or the European Patent Organization (“EPO”) member states, for any challenge to our patent rights in that country or any EPO member state, respectively, by Servier. Servier also has a unilateral right to terminate the agreement for the European Union (“EU”) or for non-EU countries, on a country-by-country basis, or in its entirety, in each case with six months’ notice.

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In December 2010, we also entered into a loan agreement with Servier, which provides for an advance of up to €15.0 million and was fully funded in January 2011 with the proceeds converting to approximately $19.5 million at the January 13, 2011, Euro to U.S. dollar exchange rate. This loan is secured by an interest in our intellectual property rights to all gevokizumab indications worldwide, excluding the United States and Japan. The loan has a final maturity date in 2016; however, after a specified period prior to final maturity, the loan is required to be repaid (1) at Servier’s option, by applying up to a significant percentage of any milestone or royalty payments owed by Servier under our collaboration agreement and (2) using a significant percentage of any upfront, milestone or royalty payments we receive from any third-party collaboration or development partner for rights to gevokizumab in the United States and/or Japan. In addition, the loan becomes immediately due and payable upon certain customary events of default. At June 30, 2012, the €15.0 million outstanding principal balance under this loan agreement would have equaled approximately $18.9 million using the June 30, 2012, Euro to U.S. dollar exchange rate.

Effective in January 2012, we entered into an amended and restated agreement with Servier for the United States commercialization rights to ACEON and, upon exercise by us of an option with respect to each product, a portfolio of additional FDC product candidates where perindopril is combined with another active ingredient(s), such as a calcium channel blocker. To date we have exercised this option with respect to one FDC product. This agreement, together with a related trademark license agreement, provides us with exclusive U.S. rights to ACEON and FDC1, and options on additional FDCs. The arrangement also provides that Servier will supply to us, and we will purchase exclusively from Servier, the active ingredients in ACEON and the FDCs, in some cases for a limited period. The agreement contains customary termination rights relating to matters such as material breach by, or insolvency of, either party or, as to particular licensed products, for safety issues arising with respect to such products. Each party also has the right to terminate the arrangement if FDC1 does not receive FDA approval by December 31, 2014. Servier also has the right to terminate the arrangement if certain aspects of our commercialization strategy are not successful and Servier does not consent to an alternative strategy or, as to the FDCs, if we breach our obligations to certain of our service providers. Further, Servier may also terminate the agreement if we fail to achieve certain levels of sales of products, and do not make a specified payment in such circumstances to maintain our license, or under certain circumstances upon our change in control, if we fail to take certain actions or make certain payments.

Because Servier is an independent third party, it may be subject to different risks than we are and has significant discretion in, and different criteria for, determining the efforts and resources it will apply related to its agreements with us. Even though we have a collaborative relationship with Servier, our relationship could deteriorate or other circumstances may prevent our relationship with Servier from resulting in successful development of marketable products. If we are not able to maintain our working relationship with Servier, or if Servier does not perform under our agreements with Servier, our ability to develop and commercialize gevokizumab and the FDCs would be materially and adversely affected, as would our ability to commercialize ACEON.

We have received negative results from certain of our clinical trials, and we face uncertain results of other clinical trials of our product candidates.

Drug development has inherent risk, and we are required to demonstrate through adequate and well-controlled clinical trials that our product candidates are effective, with a favorable benefit-risk profile for use in their target profiles before we can seek regulatory approvals for their commercial use. It is possible that we may never receive regulatory approval for any of our product candidates. Even if a product candidate receives regulatory approval, the resulting product may not gain market acceptance among physicians, patients, healthcare payors and the medical community. In March 2011, we announced our Phase 2b trial of gevokizumab in Type 2 diabetes in 421 patients did not achieve the primary endpoint of reduction in hemoglobin A1c (“HbA1c”) after six monthly treatments with gevokizumab compared to placebo. In June 2011, we announced top-line trial results from our six-month Phase 2a trial of gevokizumab in Type 2 diabetes in 74 patients, and there were no differences in glycemic control between the drug and placebo groups as measured by HbA1c levels.

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Many of our product candidates, including gevokizumab and XOMA 3AB, will require significant additional research and development, extensive preclinical studies and clinical trials and regulatory approval prior to any commercial sales. This process is lengthy and expensive, often taking a number of years. As clinical results are frequently susceptible to varying interpretations that may delay, limit or prevent regulatory approvals, the length of time necessary to complete clinical trials and to submit an application for marketing approval for a final decision by a regulatory authority varies significantly. As a result, it is uncertain whether:

our future filings will be delayed;

our preclinical and clinical studies will be successful;

we will be successful in generating viable product candidates to targets;

we will be able to provide necessary additional data;

results of future clinical trials will justify further development; or

we will ultimately achieve regulatory approval for any of these product candidates.

The timing of the commencement, continuation and completion of clinical trials may be subject to significant delays relating to various causes, including completion of preclinical testing and earlier-stage clinical trials in a timely manner, engaging contract research organizations and other service providers, scheduling conflicts with participating clinicians and clinical institutions, difficulties in identifying and enrolling patients who meet trial eligibility criteria, and shortages of available drug supply. Patient enrollment is a function of many factors, including the size of the patient population, the proximity of patients to clinical sites, the eligibility criteria for the trial, the existence of competing clinical trials and the availability of alternative or new treatments. Regardless of the initial size or relative complexity of a clinical trial, the costs of such trial may be higher than expected due to increases in duration or size of the trial, changes in the protocol pursuant to which the trial is being conducted, additional or special requirements of one or more of the healthcare centers where the trial is being conducted, changes in the regulatory requirements applicable to the trial or in the standards or guidelines for approval of the product candidate being tested or for other unforeseen reasons. In addition, we conduct clinical trials in foreign countries which may subject us to further delays and expenses as a result of increased drug shipment costs, additional regulatory requirements and the engagement of foreign clinical research organizations, as well as expose us to risks associated with foreign currency transactions insofar as we might desire to use U.S. dollars to make contract payments denominated in the foreign currency where the trial is being conducted.

All of our product candidates are prone to the risks of failure inherent in drug development. Preclinical studies may not yield results that satisfactorily support the filing of an Investigational New Drug application (“IND”) (or a foreign equivalent) with respect to our product candidates. Even if these applications would be or have been filed with respect to our product candidates, the results of preclinical studies do not necessarily predict the results of clinical trials. Similarly, early-stage clinical trials in healthy volunteers do not predict the results of later-stage clinical trials, including the safety and efficacy profiles of any particular product candidates. In addition, there can be no assurance that the design of our clinical trials is focused on appropriate indications, patient populations, dosing regimens or other variables which will result in obtaining the desired efficacy data to support regulatory approval to commercialize the drug. Preclinical and clinical data can be interpreted in different ways. Accordingly, FDA officials or officials from foreign regulatory authorities could interpret the data in different ways than we or our collaboration or development partners do which could delay, limit or prevent regulatory approval.

Administering any of our products or potential products may produce undesirable side effects, also known as adverse effects. Toxicities and adverse effects that we have observed in preclinical studies for some compounds in a particular research and development program may occur in preclinical studies or clinical trials of other compounds from the same program. Such toxicities or adverse effects could delay or prevent the filing of an IND (or a foreign equivalent) with respect to such products or potential products or cause us to cease clinical trials with respect to any drug candidate. In clinical trials, administering any of our products or product candidates to humans may produce adverse effects. These adverse effects could interrupt, delay or halt clinical trials of our products and product candidates and could result in the FDA or other regulatory authorities denying approval of our products or product candidates for any or all targeted indications. The FDA, other regulatory authorities, our collaboration or development partners or we may suspend or terminate clinical trials at any time. Even if one or more of our product candidates were approved for sale, the occurrence of even a limited number of toxicities or adverse effects when used in large populations may cause the FDA to impose restrictions on, or stop, the further marketing of such drugs. Indications of potential adverse effects or toxicities that may occur in clinical trials and that we believe are not significant during the course of such clinical trials may turn out later actually to constitute serious adverse effects or toxicities when a drug has been used in large populations or for extended periods of time. Any failure or significant delay in completing preclinical studies or clinical trials for our product candidates, or in receiving and maintaining regulatory approval for the sale of any drugs resulting from our product candidates, may severely harm our reputation and business.

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In June 2011, Novartis announced that an advisory committee of the FDA voted in favor of the overall efficacy but not the overall safety of Ilaris® (canakinumab), a fully-human monoclonal antibody that, like gevokizumab, targets IL-1 beta, to treat gouty arthritis attacks in patients who cannot obtain adequate relief with non-steroidal anti-inflammatory drugs or colchicine. Ilaris was initially approved in June 2009 for Cryopyrin-Associated Periodic Syndromes, an orphan indication. Novartis also stated that in two pivotal Phase 3 studies of canakinumab in gouty arthritis patients, a higher percentage of patients had adverse events with canakinumab than with the standard treatment for gouty arthritis, and more serious adverse events were reported by patients treated with canakinumab compared to patients receiving the standard treatment. In August 2011, Novartis announced the FDA had issued a Complete Response Letter requesting additional information, including clinical data to evaluate the benefit risk profile of canakinumab in refractory gouty arthritis patients. We have not yet determined what impact, if any, these developments may have on the development of gevokizumab.

If our therapeutic product candidates do not receive regulatory approval, neither our third-party collaborators, our contract manufacturers nor we will be able to manufacture and market them.

Our product candidates (including gevokizumab, FDC1, XMetA, XMetD, XMetS, and XOMA 3AB) cannot be manufactured and marketed in the United States or any other countries without required regulatory approvals. The United States government and governments of other countries extensively regulate many aspects of our product candidates, including:

clinical development and testing;

manufacturing;

labeling;

storage;

record-keeping;

promotion and marketing; and

importing and exporting.

In the United States, the FDA regulates pharmaceutical products under the Federal Food, Drug, and Cosmetic Act and other laws, including, in the case of biologics, the Public Health Service Act. At the present time, we believe many of our product candidates (including gevokizumab , XMetA, XMetD, XMetS, and XOMA 3AB) will be regulated by the FDA as biologics and that some of our product candidates (including FDC1) will be regulated by the FDA as drugs. Initiation of clinical trials requires approval by health authorities. Clinical trials involve the administration of the investigational new drug to healthy volunteers or to patients under the supervision of a qualified principal investigator. Clinical trials must be conducted in accordance with FDA and International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use Good Clinical Practices and the European Clinical Trials Directive under protocols that detail the objectives of the study, the parameters to be used to monitor safety and the efficacy criteria to be evaluated. Other national, foreign and local regulations also may apply. The developer of the drug must provide information relating to the characterization and controls of the product before administration to the patients participating in the clinical trials. This requires developing approved assays of the product to test before administration to the patient and during the conduct of the trial. In addition, developers of pharmaceutical products must provide periodic data regarding clinical trials to the FDA and other health authorities, and these health authorities may issue a clinical hold upon a trial if they do not believe, or cannot confirm, that the trial can be conducted without unreasonable risk to the trial participants. We cannot assure you that U.S. and foreign health authorities will not issue a clinical hold with respect to any of our clinical trials in the future.

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The results of the preclinical studies and clinical testing, together with chemistry, manufacturing and controls information, are submitted to the FDA and other health authorities in the form of an NDA for a drug, and in the form of a Biologic License Application (“BLA”) for a biological product, requesting approval to commence commercial sales. In responding to an NDA or BLA, the FDA or foreign health authorities may grant marketing approvals, request additional information or further research, or deny the application if it determines that the application does not satisfy its regulatory approval criteria. Regulatory approval of an NDA, BLA, or supplement is never guaranteed, the approval process can take several years, is extremely expensive and can vary substantially based upon the type, complexity, and novelty of the products involved, as well as the target indications. FDA regulations and policies permit applicants to request accelerated or priority review pathways for products intended to treat certain serious or life-threatening illnesses in certain circumstances. If granted by the FDA, these review pathways can provide a shortened timeline to commercialize the product, although the shortened review timeline is often accompanied with additional post-market requirements. Although we may pursue the FDA’s accelerated or priority review programs, we cannot guarantee that the FDA will permit us to utilize these pathways or that the FDA’s review of our application will not be delayed. Moreover, even if the FDA agrees to an accelerated or priority review of any of our applications, we may not ultimately be able to obtain approval of our application in a timely fashion or at all. The FDA and foreign health authorities have substantial discretion in the drug and biologics approval processes. Despite the time and expense incurred, failure can occur at any stage, and we could encounter problems that cause us to abandon clinical trials or to repeat or perform additional preclinical, clinical or manufacturing-related studies.

Changes in the regulatory approval policy during the development period, changes in, or the enactment of additional regulations or statutes, or changes in regulatory review for each submitted product application may cause delays in the approval or rejection of an application. State regulations may also affect our proposed products.

The FDA and other regulatory agencies have substantial discretion in both the product approval process and manufacturing facility approval process and, as a result of this discretion and uncertainties about outcomes of testing, we cannot predict at what point, or whether, the FDA or other regulatory agencies will be satisfied with our or our collaborators’ submissions or whether the FDA or other regulatory agencies will raise questions that may be material and delay or preclude product approval or manufacturing facility approval. In light of this discretion and the complexities of the scientific, medical and regulatory environment, our interpretation or understanding of the FDA’s or other regulatory agencies’ requirements, guidelines or expectations may prove incorrect, which could also further delay or increase the cost of the approval process. As we accumulate additional clinical data, we will submit it to the FDA and other regulatory agencies, as appropriate and such data may have a material impact on the approval process.

Given that regulatory review is an interactive and continuous process, we maintain a policy of limiting announcements and comments upon the specific details of regulatory review of our product candidates, subject to our obligations under the securities laws, until definitive action is taken.

We rely on third parties to provide services in connection with our product candidate development and manufacturing programs. The inadequate performance by or loss of any of these service providers could affect our product candidate development.

Several third parties provide services in connection with our preclinical and clinical development programs, including in vitro and in vivo studies, assay and reagent development, immunohistochemistry, toxicology, pharmacokinetics, clinical trial support, manufacturing and other outsourced activities. If these service providers do not adequately perform the services for which we have contracted or cease to continue operations and we are not able to quickly find a replacement provider or we lose information or items associated with our product candidates, our development programs may be delayed. In particular, we have a master services agreement with a CRO that provides the majority of our clinical trial services with respect to our collaboration with Servier in relation to the FDC products. Under this agreement, which was amended in October 2011, we are obligated to fund the clinical trial services provided by the CRO by allocating a specified portion of the revenue received from sales of ACEON. If we do not receive sufficient revenue from sales of ACEON to fund such services, and we do not otherwise pay the CRO for these services, certain of our rights under the commercialization agreement with Servier may terminate, unless Servier elects to make such payments on our behalf, in which case we will be required to reimburse Servier for such payments within a specified timeframe. Certain rights under the commercialization agreement with Servier will also terminate if we fail to reimburse Servier within such period.

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We may not obtain orphan drug exclusivity or we may not receive the full benefit of orphan drug exclusivity even if we obtain such exclusivity.

The FDA has awarded orphan drug status to gevokizumab for the treatment of non-infectious, intermediate, posterior or pan uveitis, or chronic non-infectious anterior uveitis and Behçet’s disease. Under the Orphan Drug Act, the first company to receive FDA approval for gevokizumab for the designated orphan drug indication will obtain seven years of marketing exclusivity during which the FDA may not approve another company’s application for gevokizumab for the same orphan indication. Even though we have obtained orphan drug designation for certain indications for gevokizumab and even if we obtain orphan drug designation for our future product candidates or other indications, due to the uncertainties associated with developing pharmaceutical products, we may not be the first to obtain marketing approval for any particular orphan indication or we may not obtain approval for an indication for which we have obtained orphan drug designation. Further, even if we obtain orphan drug exclusivity for a product, that exclusivity may not effectively protect the product from competition because different drugs can be approved for the same condition. Even after an orphan drug is approved, the FDA can subsequently approve the same drug for the same condition if the FDA concludes that the later drug is safer, more effective or makes a major contribution to patient care. Orphan drug designation neither shortens the development time or regulatory review time of a drug, nor gives the drug any advantage in the regulatory review or approval process.

Even once approved, a product may be subject to additional testing or significant marketing restrictions, its approval may be withdrawn or it may be voluntarily taken off the market.

Even if we receive regulatory approval for our product candidates, we will be subject to ongoing regulatory oversight and review by the FDA and other regulatory entities. The FDA, the European Commission or another regulatory agency may impose, as a condition of the approval, ongoing requirements for post-approval studies or post-approval obligations, including additional research and development and clinical trials, and the FDA, European Commission or other regulatory agency may subsequently withdraw approval based on these additional trials. As the current holder of the ACEON ® NDA, we are required to submit annual reports to the FDA and are responsible for pharmacovigilance activities related to the product.

Even for approved products, the FDA, European Commission or other regulatory agency may impose significant restrictions on the indicated uses, conditions for use, labeling, advertising, promotion, marketing and/or production of such product. In addition, the labeling, packaging, adverse event reporting, storage, advertising, promotion and record-keeping for our products will be subject to extensive regulatory requirements.

Furthermore, a marketing approval of a product may be withdrawn by the FDA, the European Commission or another regulatory agency or such a product may be withdrawn voluntarily by the company marketing it based, for example, on subsequently arising safety concerns. In February 2009, the European Medicines Agency (“EMA”) announced it had recommended suspension of the marketing authorization of RAPTIVA® in the European Union and its Committee for Medicinal Products for Human Use (“CHMP”) had concluded the benefits of RAPTIVA no longer outweigh its risks because of safety concerns, including the occurrence of progressive multifocal leukoencephalopathy (“PML”) in patients taking the medicine. In the second quarter of 2009, Genentech announced and carried out a phased voluntary withdrawal of RAPTIVA from the U.S. market, based on the association of RAPTIVA with an increased risk of PML. We had previously manufactured RAPTIVA.

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The FDA, European Commission and other agencies also may impose various civil or criminal sanctions for failure to comply with regulatory requirements, including product recalls or seizures, or withdrawal of product approval.

We may not be successful in commercializing our products, which could also affect our development efforts.

We began commercializing our first product, ACEON, in January 2012, and we have limited experience in the sales, marketing and distribution of pharmaceutical products. There can be no assurance that we will be able to maintain the arrangements we have with third-party suppliers, distributors and other service providers that are necessary for us to perform these activities or that our efforts will be successful. Maintaining or expanding these arrangements, or developing our own capabilities, may divert attention and resources from or otherwise negatively affect our development programs.

Our rights to commercialize ACEON are licensed from Servier, and we are obligated to use diligent efforts to develop and commercialize the products covered by our agreement in accordance with the terms and conditions of that agreement. Our ability to satisfy some of these obligations is dependent on factors that are outside of our control. Our agreement with Servier may be terminated by Servier if we materially breach our obligations and fail to cure such breach, for our insolvency, or terminated by either party with respect to any individual licensed product in the event of certain safety issues are presented. Each party also has the right to terminate the agreement if FDC1 does not receive FDA approval by December 31, 2014, and Servier may terminate the agreement if we fail to achieve certain levels of annual net sales of products, and do not make a specified payment to maintain our license. Servier also has the right to terminate the agreement if we do not meet specified commercialization objectives and Servier does not consent to an alternative strategy or, as to the FDCs, if we breach our obligations to certain of our service providers. Servier may also terminate under certain circumstances upon our change in control, if we fail to take certain actions or make certain payments. If our agreement is terminated, we would have no further rights to develop and commercialize these products.

Furthermore, because we intend to use revenues generated by sales of ACEON in part to fund development of FDC1, lower than expected revenues from such sales could adversely affect our ability to fund the costs of, and progress, such development.

We are subject to various state and federal healthcare related laws and regulations that may impact the commercialization of ACEON or our product candidates and could subject us to significant fines and penalties.

Our operations may be directly or indirectly subject to various state and federal healthcare laws, including, without limitation, the federal Anti-Kickback Statute, the federal False Claims Act and HIPAA/HITECH. These laws may impact, among other things, the commercial operations for ACEON or any of our product candidates that may be approved for commercial sale.

The federal Anti-Kickback Statute prohibits persons from knowingly and willfully soliciting, offering, receiving or providing remuneration, directly or indirectly, in exchange for or to induce either the referral of an individual, or the furnishing or arranging for a good or service, for which payment may be made under a federal healthcare program such as the Medicare and Medicaid programs. Several courts have interpreted the statute’s intent requirement to mean that if any one purpose of an arrangement involving remuneration is to induce referrals of federal healthcare covered business, the statute has been violated. The Anti-Kickback Statute is broad and prohibits many arrangements and practices that are lawful in businesses outside of the healthcare industry. Penalties for violations of the federal Anti-Kickback Statute include criminal penalties and civil sanctions such as fines, penalties, imprisonment and possible exclusion from Medicare, Medicaid and other federal healthcare programs. Many states have also adopted laws similar to the federal Anti-Kickback Statute, some of which apply to the referral of patients for healthcare items or services reimbursed by any source, not only the Medicare and Medicaid programs. The Physician Payments Sunshine Act also has several state equivalents, which require, and under which the federal government will require in 2013, disclosure of payments or other transfers of value we make to physicians.

The federal False Claims Act prohibits persons from knowingly filing, or causing to be filed, a false claim to, or the knowing use of false statements to obtain payment from the federal government. Suits filed under the False Claims Act, known as “qui tam” actions, can be brought by any individual on behalf of the government and such individuals, commonly known as “whistleblowers,” may share in any amounts paid by the entity to the government in fines or settlement. The filing of qui tam actions has caused a number of pharmaceutical, medical device and other healthcare companies to have to defend a False Claims Act action. When an entity is determined to have violated the False Claims Act, it may be required to pay up to three times the actual damages sustained by the government, plus civil penalties for each separate false claim. Various states have also enacted laws modeled after the federal False Claims Act.

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The Federal Health Insurance Portability and Accountability Act of 1996 (“HIPAA”), created new federal criminal statutes that prohibit executing a scheme to defraud any healthcare benefit program and making false statements relating to healthcare matters and was amended by the Health Information Technology and Clinical Health Act (“HITECH”), and its implementing regulations, which imposes certain requirements relating to the privacy, security and transmission of individually identifiable health information. Although we take our obligation to maintain our compliance with these various laws and regulations seriously, if we are found to be in violation of any of the laws and regulations described above or other applicable state and federal healthcare fraud and abuse laws, we may be subject to penalties, including civil and criminal penalties, damages, fines, exclusion from government healthcare reimbursement programs and the curtailment or restructuring of our operations, all of which could have a material adverse effect on our business and results of operations.

Certain of our technologies are in-licensed from third parties, so our capabilities using them are restricted and subject to additional risks.

We license technologies from third parties. These technologies include but are not limited to phage display technologies licensed to us in connection with our bacterial cell expression technology licensing program. However, our use of these technologies is limited by certain contractual provisions in the licenses relating to them and, although we have obtained numerous licenses, intellectual property rights in the area of phage display are particularly complex. If the owners of the patent rights underlying the technologies we license do not properly maintain or enforce those patents, our competitive position and business prospects could be harmed. Our success will depend in part on the ability of our licensors to obtain, maintain and enforce our in-licensed intellectual property. Our licensors may not successfully prosecute the patent applications to which we have licenses, or our licensors may fail to maintain existing patents. They may determine not to pursue litigation against other companies that are infringing these patents, or they may pursue such litigation less aggressively than we would. Our licensors also may seek to terminate our license, which could cause us to lose the right to use the licensed intellectual property and adversely affect our ability to commercialize our technologies, products or services.

We do not know whether there will be, or will continue to be, a viable market for the products in which we have an ownership or royalty interest.

Even if products in which we have an interest receive approval in the future, they may not be accepted in the marketplace. In addition, we or our collaborators or licensees may experience difficulties in launching new products, many of which are novel and based on technologies that are unfamiliar to the healthcare community. We have no assurance that healthcare providers and patients will accept such products, if developed. For example, physicians and/or patients may not accept a product for a particular indication because it has been biologically derived (and not discovered and developed by more traditional means) or if no biologically derived products are currently in widespread use in that indication. Similarly, physicians may not accept a product if they believe other products to be more effective or more cost effective or are more comfortable prescribing other products.

Safety concerns also may arise in the course of on-going clinical trials or patient treatment as a result of adverse events or reactions. For example, in February 2009, the European Medicines Agency (“EMA”) announced it had recommended suspension of the marketing authorization of RAPTIVA in the European Union and EMD Serono Inc., the company that marketed RAPTIVA in Canada (“EMD Serono”) announced that in consultation with Health Canada, the Canadian health authority (“Health Canada”), it would suspend marketing of RAPTIVA in Canada. In March 2009, Merck Serono Australia Pty Ltd, the company that marketed RAPTIVA in Australia (“Merck Serono Australia”), following a recommendation from the Therapeutic Goods Administration, the Australian health authority (“TGA”), announced it was withdrawing RAPTIVA from the Australian market. In the second quarter of 2009, Genentech announced and carried out a phased voluntary withdrawal of RAPTIVA from the U.S. market, based on the association of RAPTIVA with an increased risk of PML, and sales of the product ceased.

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Furthermore, government agencies, as well as private organizations involved in healthcare, from time to time publish guidelines or recommendations to healthcare providers and patients. Such guidelines or recommendations can be very influential and may adversely affect the usage of any products we may develop directly (for example, by recommending a decreased dosage of a product in conjunction with a concomitant therapy or a government entity withdrawing its recommendation to screen blood donations for certain viruses) or indirectly (for example, by recommending a competitive product over our product). Consequently, we do not know if physicians or patients will adopt or use our products for their approved indications.

Even approved and marketed products are subject to risks relating to changes in the market for such products. Introduction or increased availability of generic versions of products can alter the market acceptance of branded products, such as ACEON. In addition, unforeseen safety issues may arise at any time, regardless of the length of time a product has been on the market.

Our third-party collaborators, licensees, suppliers or contractors may not have adequate manufacturing capacity sufficient to meet market demand.

Upon approval of any of our product candidates or in the event of increased demand for marketed products, we do not know whether the capacity of the manufacturing facilities of our existing or future third-party collaborators, licensees, suppliers or contractors will be available or can be increased to produce sufficient quantities of our products to meet market demand. Also, if we or our third-party collaborators, licensees, suppliers or contractors need additional manufacturing facilities to meet market demand, we cannot predict that we will successfully obtain those facilities because we do not know whether they will be available on acceptable terms. In addition, any manufacturing facilities acquired or used to meet market demand must meet the FDA’s quality assurance guidelines.

In addition to our agreements with Servier, our agreements with other third parties, many of which are significant to our business, expose us to numerous risks.

Our financial resources and our marketing experience and expertise are limited. Consequently, our ability to successfully develop products depends, to a large extent, upon securing the financial resources and/or marketing capabilities of third parties other than Servier. For example:

In March 2004, we announced we had agreed to collaborate with Chiron Corporation (now Novartis) for the development and commercialization of antibody products for the treatment of cancer. In April 2005, we announced the initiation of clinical testing of the first product candidate out of the collaboration, HCD122, an anti-CD40 antibody, in patients with advanced chronic lymphocytic leukemia. In October 2005, we announced the initiation of the second clinical trial of HCD122 in patients with multiple myeloma. In November 2008, we announced the restructuring of this product development collaboration, which involved six development programs including the ongoing HCD122 and LFA102 programs. In exchange for cash and debt reduction on our existing loan facility with Novartis, Novartis has control over the HCD122 and LFA102 programs, as well as the right to expand the development of these programs into additional indications outside of oncology.

In March 2005, we entered into a contract with the National Institute of Allergy and Infectious Diseases (“NIAID”) to produce three monoclonal antibodies designed to protect U.S. citizens against the harmful effects of botulinum neurotoxin used in bioterrorism. In July 2006, we entered into an additional contract with NIAID for the development of an appropriate formulation for human administration of these three antibodies in a single injection. In September 2008, we announced that we were awarded an additional contract with NIAID to support our on-going development of drug candidates toward clinical trials in the treatment of botulism poisoning. In October 2011, we announced we had been awarded an additional contract with NIAID to develop broad-spectrum antitoxins for the treatment of human botulism poisoning.

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In December 2011, we entered into a loan agreement with GECC, under which GECC agreed to make a term loan in an aggregate principal amount of $10 million to XOMA (US) LLC, our wholly owned subsidiary, and upon execution of the loan agreement, GECC funded the term loan. The term loan is guaranteed by us and our two other principal subsidiaries, XOMA Ireland Limited and XOMA Technology Ltd. As security for our obligations under the loan agreement, we, XOMA (US) LLC, XOMA Ireland Limited and XOMA Technology Ltd. each granted a security interest pursuant to a guaranty, pledge and security agreement in substantially all of our existing and after-acquired assets, excluding our intellectual property assets (such as those relating to our gevokizumab and anti-botulism products). We were required to repay the principal amount of the Term Loan over a period of 42 installments of principal and accrued interest, but amended the loan agreement on September 27, 2012, as described below. The loan agreement contains customary representations and warranties and customary affirmative and negative covenants, including restrictions on the ability to incur indebtedness, grant liens, make investments, dispose of assets, enter into transactions with affiliates and amend existing material agreements, in each case subject to various exceptions. In addition, the loan agreement contains customary events of default that entitle GECC to cause any or all of the indebtedness under the loan agreement to become immediately due and payable. The events of default include any event of default under a material agreement or certain other indebtedness. We may voluntarily prepay the term loan in full, but not in part, and any voluntary and certain mandatory prepayments are subject to a prepayment premium of 3% in the first year of the loan, 2% in the second year and 1% thereafter, with certain exceptions. We will also be required to pay the Final Payment Fee in connection with any voluntary or mandatory prepayment. Pursuant to the loan agreement, we issued to GECC unregistered stock purchase warrants, which entitle GECC to purchase up to an aggregate of 263,158 unregistered shares of XOMA common stock at an exercise price equal to $1.14 per share, are immediately exercisable and expire on December 30, 2016.

On September 27, 2012, we entered into an amendment to the loan agreement providing for an additional term loan in the amount of $4,642,857, and an extension of the interest-only monthly repayment period with respect to the aggregate loan obligation of $12,500,000 outstanding following the effective date of the amendment through March 1, 2013, at a stated interest rate of 10.9% per annum. Thereafter, we are obligated to make monthly principal payments of $347,222, plus accrued interest, at a stated interest rate of 10.9% per annum, over a 27-month period commencing on April 1, 2013 and through June 15, 2015, at which time the remaining outstanding principal amount of $3,125,000, plus accrued interest, shall be due. A final payment fee in the amount of $875,000 is payable on the date upon which the outstanding principal amount is required to be repaid in full. Any mandatory or voluntary prepayment of the $12,500,000 will accelerate the due date of the final payment fee, and trigger a prepayment penalty equal to 3% of the outstanding principal amount being prepaid if prepaid on or before September 27, 2013, 2% if prepaid on or before September 27, 2014, and 1% if prepaid after September 27, 2014, but prior to the maturity date. In connection with the amendment, on September 27, 2012 we issued GE a warrant to purchase up to 39,346 shares of our common stock, which warrant is exercisable immediately, has a five year term and has an exercise price of $3.54 per share.

We have licensed our bacterial cell expression technology, an enabling technology used to discover and screen, as well as develop and manufacture, recombinant antibodies and other proteins for commercial purposes, to over 60 companies. As of October 23, 2012, we were aware of two antibody products manufactured using this technology that have received FDA approval, Genentech’s LUCENTIS (ranibizumab injection) for treatment of neovascular wet age-related macular degeneration and UCB’s CIMZIA (certolizumab pegol) for treatment of Crohn’s disease and rheumatoid arthritis. In the third quarter of 2009, we sold our LUCENTIS royalty interest to Genentech. In the third quarter of 2010, we sold our CIMZIA royalty interest.

On July 24, 2012, we and Servier entered into an agreement with Boehringer Ingelheim to transfer XOMA's technology and processes for the manufacture of gevokizumab to Boehringer lngetheim, for Boehringer Ingelheim's implementation and validation in preparation for the commercial manufacture of gevokizumab. Upon the successful completion of the transfer and the establishment of biological comparability, including validation of the XOMA processes as implemented by Boehringer Ingelheim, it is our intention that Boehringer Ingelheim will produce gevokizumab for XOMA's commercial use at its facility in Biberach, Germany. We and Servier retain all rights to the development and commercialization of gevokizumab. Transfer of our technology to Boehringer Ingelheim exposes us to numerous risks, including the possibility that Boehringer Ingelheim may not perform under the agreement as anticipated, and that we will need to successfully conduct a comparability trial demonstrating to the FDA’s satisfaction the similarity between XOMA manufactured and Boehringer Ingelheim manufactured product.

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Because our collaborators, licensees, suppliers and contractors are independent third parties, they may be subject to different risks than we are and have significant discretion in, and different criteria for, determining the efforts and resources they will apply related to their agreements with us. If these collaborators, licensees, suppliers and contractors do not successfully perform the functions for which they are responsible, we may not have the capabilities, resources or rights to do so on our own.

We do not know whether we, our collaborators or licensees will successfully develop and market any of the products that are or may become the subject of any of our collaboration or licensing arrangements. In some cases these arrangements provide for funding solely by our collaborators or licensees, and in other cases, all of the funding for certain projects and a significant portion of the funding for other projects is to be provided by our collaborator or licensee, and we provide the balance of the funding. Even when we have a collaborative relationship, other circumstances may prevent it from resulting in successful development of marketable products. In addition, third-party arrangements such as ours also increase uncertainties in the related decision-making processes and resulting progress under the arrangements, as we and our collaborators or licensees may reach different conclusions, or support different paths forward, based on the same information, particularly when large amounts of technical data are involved. Furthermore, our contracts with NIAID contain numerous standard terms and conditions provided for in the applicable federal acquisition regulations and customary in many government contracts, some of which could allow the U.S. government to exercise certain rights under the technology developed under these contracts. Uncertainty exists as to whether we will be able to comply with these terms and conditions in a timely manner, if at all. In addition, we are uncertain as to the extent of NIAID’s demands and the flexibility that will be granted to us in meeting those demands.

Although we continue to evaluate additional strategic alliances and potential partnerships, we do not know whether or when any such alliances or partnerships will be entered into.

Products and technologies of other companies may render some or all of our products and product candidates noncompetitive or obsolete.

Developments by others may render our products, product candidates, or technologies obsolete or uncompetitive. Technologies developed and utilized by the biotechnology and pharmaceutical industries are continuously and substantially changing. Competition in antibody-based technologies is intense and is expected to increase in the future as a number of established biotechnology firms and large chemical and pharmaceutical companies advance in these fields. Many of these competitors may be able to develop products and processes competitive with or superior to our own for many reasons, including that they may have:

significantly greater financial resources;

larger research and development and marketing staffs;

larger production facilities;

entered into arrangements with, or acquired, biotechnology companies to enhance their capabilities; or

extensive experience in preclinical testing and human clinical trials.

These factors may enable others to develop products and processes competitive with or superior to our own or those of our collaborators. In addition, a significant amount of research in biotechnology is being carried out in universities and other non-profit research organizations. These entities are becoming increasingly interested in the commercial value of their work and may become more aggressive in seeking patent protection and licensing arrangements. Furthermore, many companies and universities tend not to announce or disclose important discoveries or development programs until their patent position is secure or, for other reasons, later; as a result, we may not be able to track development of competitive products, particularly at the early stages. Positive or negative developments in connection with a potentially competing product may have an adverse impact on our ability to raise additional funding on acceptable terms. For example, if another product is perceived to have a competitive advantage, or another product’s failure is perceived to increase the likelihood that our product will fail, then investors may choose not to invest in us on terms we would accept or at all.

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The examples below pertain to competitive events in the market which we review quarterly and are not intended to be representative of all existing competitive events.

Gevokizumab

We, in collaboration with Servier, are developing gevokizumab, an anti-inflammatory monoclonal antibody targeting IL-1 beta. Other companies are developing other products based on the same or similar therapeutic targets as gevokizumab and these products may prove more effective than gevokizumab. We are aware that:

Novartis markets and is developing Ilaris (canakinumab, ACZ885), a fully human monoclonal antibody that selectively binds to and neutralizes IL-1 beta. Since 2009, canakinumab has been approved in over 50 countries for the treatment of children and adults suffering from Cryopyrin-Associated Periodic Syndrome (“CAPS”). Novartis has filed for regulatory approval of canakinumab in the United States and Europe for the treatment of acute attacks in gouty arthritis. In August 2011, Novartis announced that the FDA had issued a Complete Response Letter requesting additional information, including clinical data to evaluate the benefit risk profile of canakinumab in refractory gouty arthritis patients. In September 2011, Novartis announced positive results of a pivotal Phase 3 trial of canakinumab in patients with systemic juvenile idiopathic arthritis and that it plans to seek regulatory approval for this indication in 2012. Novartis is also pursuing other diseases in which IL-1 beta may play a prominent role, such as systemic secondary prevention of cardiovascular events.

Eli Lilly and Company (“Lilly”) is developing a monoclonal antibody to IL-1 beta in Phase 1 development for the treatment of cardiovascular disease. In June 2011, Lilly reported results from a Phase 2 study of LY2189102 in 106 patients with Type 2 diabetes, showing a significant (p<0.05), early reduction in C reactive protein, moderate reduction in HbA1c and anti-inflammatory effects. We do not know whether LY2189102 remains in development.

In 2008, Swedish Orphan Biovitrum obtained from Amgen the global exclusive rights to Kineret® (anakinra) for rheumatoid arthritis as currently indicated in its label. In November 2009, the agreement regarding Swedish Orphan Biovitrum’s Kineret license was expanded to include certain orphan indications. Kineret is an IL-1 receptor antagonist (IL-1ra) which has been evaluated in multiple IL-1 mediated diseases, including indications we are considering for gevokizumab. In addition to other on-going studies, a proof-of-concept clinical trial in the United Kingdom investigating Kineret in patients with a certain type of myocardial infarction, or heart attack, has been completed. In August 2010, Biovitrum announced the FDA had granted orphan drug designation to Kineret for the treatment of CAPS.

In February 2008, Regeneron Pharmaceuticals, Inc. (“Regeneron”) announced it had received marketing approval from the FDA for ARCALYST® (rilonacept) Injection for Subcutaneous Use, an interleukin-1 blocker or IL-1 Trap, for the treatment of CAPS, including Familial Cold Auto-inflammatory Syndrome and Muckle-Wells Syndrome in adults and children 12 and older. In September 2009, Regeneron announced rilonacept was approved in the European Union for CAPS. In June 2010 and February 2011, Regeneron announced positive results of two Phase 3 clinical trials of rilonacept in gout. In November 2011, Regeneron announced the FDA had accepted for review Regeneron’s supplemental BLA for ARCALYST for the prevention and treatment of gout. A meeting of an FDA advisory panel to review this supplemental BLA was held in May 2012 with a recommendation against approval of the new use in gout. In July 2012, the FDA issued a complete response letter that states the FDA cannot approve the application in its current form and has requested additional clinical data, as well as additional CMC information related to a proposed new dosage form. Regeneron is reviewing the complete response letter from the FDA and will determine appropriate next steps.

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Amgen has been developing AMG 108, a fully human monoclonal antibody that targets inhibition of the action of IL-1. In April 2008, Amgen discussed results from a Phase 2 study in rheumatoid arthritis. AMG 108 showed statistically significant improvement in the signs and symptoms of rheumatoid arthritis and was well tolerated. In January 2011, MedImmune, the worldwide biologics unit for AstraZeneca PLC, announced Amgen granted it rights to develop AMG 108 worldwide except in Japan.

In June 2009, Cytos Biotechnology AG announced the initiation of an ascending dose Phase 1/2a study of CYT013-IL1bQb, a therapeutic vaccine targeting IL-1 beta, in Type 2 diabetes. In 2010, this study was extended to include two additional groups of patients.

We are aware that the following companies have completed or are conducting or planning Phase 3 clinical trials of the following products for the treatment of intermediate, posterior or pan-noninfectious uveitis: Abbott - HUMIRA® (adalimumab); Lux Biosciences, Inc. – LUVENIQ® (voclosporin); Novartis - Myfortic® (mycophenalate sodium) and Santen Pharmaceutical Co., Ltd. – Sirolimus® (rapamycin).

Perindopril

We are currently selling ACEON, an angiotensin converting enzyme (“ACE”) inhibitor, and developing FDC1, a combination of perindopril arginine and amlodipine besylate.

The ACE inhibitor market is highly genericized with all options being available generically. We are aware that:

The number one product (based on annual sales) in the United States within the ACE inhibitor category is lisinopril, formerly marketed by Astra-Zeneca Pharmaceuticals LP under the brand ZESTRIL® and by Merck & Co. under the brand Prinivil®.

There are multiple options in the fixed-dose combination market combining ACE inhibitors with diuretics, and two options combining an ACE inhibitor with a calcium channel blocker. Current options with a calcium channel blocker are benazepril/amlodipine, formerly marketed by Novartis Pharmaceuticals as Lotrel® , and trandolapril/verapamil, formerly marketed by Abbot Laboratories as Tarka®.

ACE inhibitors are a segment of the larger Renin Angiotensin Aldosterone System (“RAAS”) market. This market is comprised of ACE inhibitors and angiotensin receptor blockers (“ARB”). Both classes act on the RAAS in different ways to control blood pressure. We are aware that the most successful of the ARB (in terms of annual sales) is valsartan, trade name Diovan®, which is marketed by Novartis. This compound, along with other ARBs, has been developed in multiple fixed-dose combination products: with a diuretic, a calcium channel blocker (amlodipine) and as a triple combination of all three.

Our perindopril franchise will compete directly with FDCs containing an ACE inhibitor and secondarily with fixed-dose combinations containing an ARB.

XOMA 3AB

We are also developing XOMA 3AB, a combination, or cocktail, of antibodies designed to neutralize the most potent of botulinum toxins. Other companies are developing other products targeting botulism poisoning and these products may prove more effective than XOMA 3AB. We are aware that:

Cangene Corporation has a contract with the U.S. Department of Health & Human Services, expected to be for $423.0 million, to manufacture and supply an equine heptavalent botulism anti-toxin; and

Emergent BioSolutions, Inc. is currently in development of a botulism immunoglobulin candidate that may compete with our anti-botulinum neurotoxin monoclonal antibodies.

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Manufacturing risks and inefficiencies may adversely affect our ability to manufacture products for ourselves or others.

To the extent we continue to provide manufacturing services for our own benefit or to third parties, we are subject to manufacturing risks. Additionally, unanticipated fluctuations in customer requirements have led and may continue to lead to manufacturing inefficiencies, which if significant could lead to an impairment on our long-lived assets or restructuring activities. We must utilize our manufacturing operations in compliance with regulatory requirements, in sufficient quantities and on a timely basis, while maintaining acceptable product quality and manufacturing costs. Additional resources and changes in our manufacturing processes may be required for each new product, product modification or customer or to meet changing regulatory or third-party requirements, and this work may not be successfully or efficiently completed.

Manufacturing and quality problems may arise in the future to the extent we continue to perform these manufacturing activities for our own benefit or for third parties. Consequently, our development goals or milestones may not be achieved in a timely manner or at a commercially reasonable cost, or at all. In addition, to the extent we continue to make investments to improve our manufacturing operations, our efforts may not yield the improvements that we expect.

Failure of our products to meet current Good Manufacturing Practices standards may subject us to delays in regulatory approval and penalties for noncompliance.

Our contract manufacturers are required to produce ACEON and our clinical product candidates under current Good Manufacturing Practices (“cGMP”) to meet acceptable standards for use in our clinical trials and for commercial sale, as applicable. If such standards change, the ability of contract manufacturers to produce ACEON and our product candidates on the schedule we require for our clinical trials or to meet commercial requirements may be affected. In addition, contract manufacturers may not perform their obligations under their agreements with us or may discontinue their business before the time required by us to successfully produce clinical and commercial supplies of ACEON and our product candidates. We and our contract manufacturers are subject to pre-approval inspections and periodic unannounced inspections by the FDA and corresponding state and foreign authorities to ensure strict compliance with cGMP and other applicable government regulations and corresponding foreign standards. We do not have control over a third-party manufacturer’s compliance with these regulations and standards. Any difficulties or delays in our contractors’ manufacturing and supply of ACEON and our product candidates or any failure of our contractors to maintain compliance with the applicable regulations and standards could increase our costs, cause us to lose revenue, make us postpone or cancel clinical trials, prevent or delay regulatory approval by the FDA and corresponding state and foreign authorities, prevent the import and/or export of ACEON and our product candidates, or cause ACEON and any of our product candidates that may be approved for commercial sale to be recalled or withdrawn.

Because many of the companies we do business with are also in the biotechnology sector, the volatility of that sector can affect us indirectly as well as directly.

As a biotechnology company that collaborates with other biotechnology companies, the same factors that affect us directly can also adversely impact us indirectly by affecting the ability of our collaborators, partners and others we do business with to meet their obligations to us and reduce our ability to realize the value of the consideration provided to us by these other companies.

For example, in connection with our licensing transactions relating to our bacterial cell expression technology, we have in the past and may in the future agree to accept equity securities of the licensee in payment of license fees. The future value of these or any other shares we receive is subject both to market risks affecting our ability to realize the value of these shares and more generally to the business and other risks to which the issuer of these shares may be subject.

As we do more business internationally, we will be subject to additional political, economic and regulatory uncertainties.

We may not be able to successfully operate in any foreign market. We believe that because the pharmaceutical industry is global in nature, international activities will be a significant part of our future business activities and that when and if we are able to generate income, a substantial portion of that income will be derived from product sales and other activities outside the United States. Foreign regulatory agencies often establish standards different from those in the United States, and an inability to obtain foreign regulatory approvals on a timely basis could put us at a competitive disadvantage or make it uneconomical to proceed with a product or product candidate’s development. International operations and sales may be limited or disrupted by:

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imposition of government controls;

export license requirements;

political or economic instability;

trade restrictions;

changes in tariffs;

restrictions on repatriating profits;

exchange rate fluctuations;

withholding and other taxation; and

difficulties in staffing and managing international operations.

We are subject to foreign currency exchange rate risks.

We are subject to foreign currency exchange rate risks because substantially all of our revenues and operating expenses are paid in U.S. dollars, but we pay interest and principal obligations with respect to our loan from Servier in Euros. To the extent that the U.S. dollar declines in value against the Euro, the effective cost of servicing our Euro-denominated debt will be higher. Changes in the exchange rate result in foreign currency gains or losses. Although we have managed some of our exposure to changes in foreign currency exchange rates by entering into foreign exchange option contracts, there can be no assurance that foreign currency fluctuations will not have a material adverse effect on our business, financial condition, liquidity or results of operations. In addition, our foreign exchange option contracts are re-valued at each financial reporting period, which may also result in gains or losses from time to time.

If we and our partners are unable to protect our intellectual property, in particular our patent protection for our principal products, product candidates and processes, and prevent its use by third parties, our ability to compete in the market will be harmed, and we may not realize our profit potential.

We rely on patent protection, as well as a combination of copyright, trade secret, and trademark laws to protect our proprietary technology and prevent others from duplicating our products or product candidates. However, these means may afford only limited protection and may not:

prevent our competitors from duplicating our products;

prevent our competitors from gaining access to our proprietary information and technology; or

permit us to gain or maintain a competitive advantage.

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Because of the length of time and the expense associated with bringing new products to the marketplace, we and our collaboration and development partners hold and are in the process of applying for a number of patents in the United States and abroad to protect our product candidates and important processes and also have obtained or have the right to obtain exclusive licenses to certain patents and applications filed by others. However, the mere issuance of a patent is not conclusive as to its validity or its enforceability. The U.S. Federal Courts or equivalent national courts or patent offices elsewhere may invalidate our patents or find them unenforceable. In addition, the laws of foreign countries may not protect our intellectual property rights effectively or to the same extent as the laws of the United States. If our intellectual property rights are not adequately protected, we may not be able to commercialize our technologies, products, or services, and our competitors could commercialize our technologies, which could result in a decrease in our sales and market share that would harm our business and operating results. Specifically, the patent position of biotechnology companies generally is highly uncertain and involves complex legal and factual questions. The legal standards governing the validity of biotechnology patents are in transition, and current defenses as to issued biotechnology patents may not be adequate in the future. Accordingly, there is uncertainty as to:

whether any pending or future patent applications held by us will result in an issued patent, or that if patents are issued to us, that such patents will provide meaningful protection against competitors or competitive technologies;

whether competitors will be able to design around our patents or develop and obtain patent protection for technologies, designs or methods that are more effective than those covered by our patents and patent applications; or

the extent to which our product candidates could infringe on the intellectual property rights of others, which may lead to costly litigation, result in the payment of substantial damages or royalties, and/or prevent us from using technology that is essential to our business.

We have established a portfolio of patents, both United States and foreign, related to our bacterial cell expression technology, including claims to novel promoter sequences, secretion signal sequences, compositions and methods for expression and secretion of recombinant proteins from bacteria, including immunoglobulin gene products. Most of the more important European patents in our bacterial cell expression patent portfolio expired in July 2008 or earlier.

If certain patents issued to others are upheld or if certain patent applications filed by others issue and are upheld, we may require licenses from others to develop and commercialize certain potential products incorporating our technology or we may become involved in litigation to determine the proprietary rights of others. These licenses, if required, may not be available on acceptable terms, and any such litigation may be costly and may have other adverse effects on our business, such as inhibiting our ability to compete in the marketplace and absorbing significant management time.

Due to the uncertainties regarding biotechnology patents, we also have relied and will continue to rely upon trade secrets, know-how and continuing technological advancement to develop and maintain our competitive position. All of our employees have signed confidentiality agreements under which they have agreed not to use or disclose any of our proprietary information. Research and development contracts and relationships between us and our scientific consultants and potential customers provide access to aspects of our know-how that are protected generally under confidentiality agreements. These confidentiality agreements may be breached or may not be enforced by a court. To the extent proprietary information is divulged to competitors or to the public generally, such disclosure may adversely affect our ability to develop or commercialize our products by giving others a competitive advantage or by undermining our patent position.

Litigation regarding intellectual property can be costly and expose us to risks of counterclaims against us.

We may be required to engage in litigation or other proceedings to protect our intellectual property. The cost to us of this litigation, even if resolved in our favor, could be substantial. Such litigation could also divert management’s attention and resources. In addition, if this litigation is resolved against us, our patents may be declared invalid, and we could be held liable for significant damages. In addition, we may be subject to a claim that we are infringing another party’s patent. If such claim is resolved against us, we or our collaborators may be enjoined from developing, manufacturing, selling or importing products, processes or services unless we obtain a license from the other party.

Such license may not be available on reasonable terms, thus preventing us from using these products, processes or services and adversely affecting our revenue.

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We may be unable to effectively price our products or obtain adequate reimbursement for sales of our products, which would prevent our products from becoming profitable.

If we or our third-party collaborators or licensees succeed in bringing our product candidates to the market, they may not be considered cost effective, and reimbursement to the patient may not be available or may not be sufficient to allow us to sell our products on a competitive basis. In both the United States and elsewhere, sales of medical products and treatments are dependent, in part, on the availability of reimbursement to the patient from third-party payors, such as government and private insurance plans. Third-party payors are increasingly challenging the prices charged for pharmaceutical products and services. Our business is affected by the efforts of government and third-party payors to contain or reduce the cost of healthcare through various means. In the United States, there have been and will continue to be a number of federal and state proposals to implement government controls on pricing.

In addition, the emphasis on managed care in the United States has increased and will continue to increase the pressure on the pricing of pharmaceutical products. We cannot predict whether any legislative or regulatory proposals will be adopted or the effect these proposals or managed care efforts may have on our business.

Healthcare reform measures and other statutory or regulatory changes could adversely affect our business.

In both the United States and certain foreign jurisdictions, there have been a number of legislative and regulatory proposals to change the healthcare system in ways that could impact our business. In March 2010, the U.S. Congress enacted and President Obama signed into law the Patient Protection and Affordable Care Act, as amended by the Health Care and Education Affordability Reconciliation Act (collectively, “PPACA”), which includes a number of healthcare reform provisions. The reforms imposed by the law are expected to significantly impact the pharmaceutical industry, most likely in the area of pharmaceutical product pricing. While the law may increase the number of patients who have insurance coverage for our products or product candidates, its cost containment measures could also adversely affect reimbursement for our existing or potential products; however, the full effects of this law cannot be known until these provisions are implemented and the relevant federal and state agencies issue applicable regulations or guidance.

The pharmaceutical and biotechnology industries are subject to extensive regulation, and from time to time legislative bodies and governmental agencies consider changes to such regulations that could have significant impact on industry participants. For example, in light of certain highly publicized safety issues regarding certain drugs that had received marketing approval, the U.S. Congress has considered various proposals regarding drug safety, including some which would require additional safety studies and monitoring and could make drug development more costly. We are unable to predict what additional legislation or regulation, if any, relating to safety or other aspects of drug development may be enacted in the future or what effect such legislation or regulation would have on our business.

Beginning in 2013, the PPACA also imposes new reporting and disclosure requirements on pharmaceutical manufacturers for payments to healthcare providers and ownership of their stock by healthcare providers. Failure to submit required information may result in civil monetary penalties of up to an aggregate of $150,000 per year (or up to an aggregate of $1 million per year for “knowing failures”), for all payments, transfers of value or ownership or investment interests not reported in an annual submission. On December 14, 2011, CMS released its proposed rule implementing these provisions, providing further clarification to ambiguous or unclear statutory language and providing instructions for manufacturers to comply with such requirements. CMS has not issued a final rule to date.

The business and financial condition of pharmaceutical and biotechnology companies are also affected by the efforts of governments, third-party payors and others to contain or reduce the costs of healthcare to consumers. In the United States and various foreign jurisdictions there have been, and we expect that there will continue to be, a number of legislative and regulatory proposals aimed at changing the healthcare system, such as proposals relating to the reimportation of drugs into the United States from other countries (where they are then sold at a lower price) and government control of prescription drug pricing. We expect that current health care reform measures such as PPACA and those that may be adopted in the future could result in a decrease in the share price of our common stock, limit our ability to raise capital or to obtain strategic collaborations or licenses, or successfully commercialize our products.

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We are exposed to the risk of product liability claims which could harm our business.

The testing, marketing and sales of medical products entails an inherent risk of allegations of product liability. We have been party to a number of product liability claims filed against Genentech Inc., and even though Genentech has agreed to indemnify us in connection with these matters, there can be no assurance that these or other products liability lawsuits will not result in liability to us or that our insurance or contractual arrangements will provide us with adequate protection against such liabilities. In the event of one or more large, unforeseen awards of damages against us, our product liability insurance may not provide adequate coverage. A significant product liability claim for which we were not covered by insurance or indemnified by a third party would have to be paid from cash or other assets, which could have an adverse effect on our business and the value of our common stock. To the extent we have sufficient insurance coverage, such a claim would result in higher subsequent insurance rates. In addition, product liability claims can have various other ramifications including loss of future sales opportunities, increased costs associated with replacing products, a negative impact on our goodwill and reputation, and divert our management’s attention from our business, each of which could also adversely affect our business and operating results.

The loss of key personnel, including our Chief Executive Officer, could delay or prevent achieving our objectives.

Our research, product development and business efforts could be adversely affected by the loss of one or more key members of our scientific or management staff, particularly our executive officers: John Varian, our Chief Executive Officer; Patrick J. Scannon, M.D., Ph.D., our Executive Vice President and Chief Scientific Officer; Fred Kurland, our Vice President, Finance and Chief Financial Officer; and Paul D. Rubin, M.D., our Senior Vice President, Research and Development and Chief Medical Officer. We currently have no key person insurance on any of our employees.

Our ability to use our net operating loss carry-forwards and other tax attributes will be substantially limited by Section 382 of the U.S. Internal Revenue Code.

Section 382 of the U.S. Internal Revenue Code of 1986, as amended, generally limits the ability of a corporation that undergoes an “ownership change” to utilize its net operating loss carry-forwards (“NOLs”) and certain other tax attributes against any taxable income in taxable periods after the ownership change. The amount of taxable income in each taxable year after the ownership change that may be offset by pre-change NOLs and certain other pre-change tax attributes is generally equal to the product of (a) the fair market value of the corporation’s outstanding shares (or, in the case of a foreign corporation, the fair market value of items treated as connected with the conduct of a trade or business in the United States) immediately prior to the ownership change and (b) the long-term tax exempt rate (i.e., a rate of interest established by the U.S. Internal Revenue Service (“IRS”) that fluctuates from month to month). In general, an “ownership change” occurs whenever the percentage of the shares of a corporation owned, directly or indirectly, by “5-percent shareholders” (within the meaning of Section 382 of the Internal Revenue Code) increases by more than 50 percentage points over the lowest percentage of the shares of such corporation owned, directly or indirectly, by such “5-percent shareholders” at any time over the preceding three years.

Based on our initial analysis under Section 382 (which subjects the amount of pre-change NOLs and certain other pre-change tax attributes that can be utilized to an annual limitation), we experienced an ownership change in 2009, which would substantially limit the future use of our pre-change NOLs and certain other pre-change tax attributes per year. We have and will continue to evaluate alternative analyses permitted under Section 382 and IRS notices to determine whether or not any ownership changes have occurred and may occur (and if so, when they occurred) that would result in limitations on our NOLs or certain other tax attributes. As a result of this offering, we expect additional limitations may be imposed on the future use of our pre-change NOLs limitations.

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We may not realize the expected benefits of our initiatives to reduce costs across our operations, and we may incur significant charges or write-downs as part of these efforts.

We have pursued and may continue to pursue a number of initiatives to reduce costs of our operations. In January 2012, we implemented a workforce reduction of approximately 34% to improve our cost structure. This workforce reduction resulted primarily from our decisions to utilize a contract manufacturing organization for Phase 3 and commercial antibody production and to eliminate internal research functions that are non-differentiating or that can be obtained cost effectively by contract service providers. As a result, we expect to reduce ongoing internal spending by approximately $14 million in 2012 compared to the 2011 level. In the first half of 2012, as a result of our streamlining of operations, we incurred restructuring and related severance costs totaling approximately $4.5 million, of which $2.4 million were cash charges. For the remainder of 2012, we do not expect to incur additional significant restructuring and severance costs.

We may not realize some or all of the expected benefits of our current and future initiatives to reduce costs. In addition to restructuring or other charges, we may experience disruptions in our operations as a result of these initiatives.

Because we are a relatively small biopharmaceutical company with limited resources, we may not be able to attract and retain qualified personnel.

Our success in developing marketable products and achieving a competitive position will depend, in part, on our ability to attract and retain qualified scientific and management personnel, particularly in areas requiring specific technical, scientific or medical expertise. We had approximately 164 employees as of August 3, 2012. We may require additional experienced executive, accounting, research and development, legal, administrative and other personnel from time to time in the future. There is intense competition for the services of these personnel, especially in California. Moreover, we expect that the high cost of living in the San Francisco Bay Area, where our headquarters and manufacturing facilities are located, may impair our ability to attract and retain employees in the future. If we do not succeed in attracting new personnel and retaining and motivating existing personnel, our operations may suffer and we may be unable to implement our current initiatives or grow effectively.

Global credit and financial market conditions may reduce our ability to access and maintain capital for our operations.

Traditionally, we have funded a large portion of our research and development expenditures through raising capital in the equity markets. Recent events, including failures and bankruptcies among large commercial and investment banks, have led to considerable declines and uncertainties in these and other capital markets and have led to new regulatory and other restrictions that may broadly affect the nature of these markets. These circumstances could severely restrict the raising of new capital by companies such as us in the future.

Volatility in the financial markets has also created liquidity problems in investments previously thought to bear a minimal risk. For example, money market fund investors, including us, have in the past been unable to retrieve the full amount of funds, even in highly-rated liquid money market accounts, upon maturity. Although as of June 30, 2012, we have received the full amount of proceeds from money market fund investments, an inability to retrieve funds from money market fund investments as they mature in the future could have a material and adverse impact on our business, results of operations and cash flows.

Our cash and cash equivalents are maintained in highly liquid investments with remaining maturities of 90 days or less at the time of purchase. While as of the date of this prospectus supplement we are not aware of any downgrades, material losses, or other significant deterioration in the fair value of our cash equivalents since June 30, 2012, no assurance can be given that further deterioration in conditions of the global credit and financial markets would not negatively impact our current portfolio of cash equivalents or our ability to meet our financing objectives.

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Our business and operations would suffer in the event of system failures.

Despite the implementation of security measures, our internal computer systems and those of our current and any future collaborators, licensees, suppliers, contractors and consultants are vulnerable to damage from cyber−attacks, computer viruses, unauthorized access, natural disasters, terrorism, war and telecommunication and electrical failures. We could experience failures in our information systems and computer servers, which could be the result of a cyber−attack and could result in an interruption of our normal business operations and require substantial expenditure of financial and administrative resources to remedy. System failures, accidents or security breaches can cause interruptions in our operations and can result in a material disruption of our development programs, commercialization activities and other business operations. The loss of clinical trial data from completed or future clinical trials could result in delays in our regulatory approval efforts and significantly increase our costs to recover or reproduce the data. Similarly, we rely on third parties to supply components for and manufacture our product and product candidates, conduct clinical trials of our product candidates and warehouse and distribute ACEON, and similar events relating to their computer systems could also have a material adverse effect on our business. To the extent that any disruption or security breach were to result in a loss of, or damage to, our data or applications, or inappropriate disclosure of confidential or proprietary information, we could incur liability and the development of gevokizumab, FDC1 or any of our other product candidates and the commercialization of ACEON could be delayed or otherwise adversely affected.

Calamities, power shortages or power interruptions at our Berkeley headquarters and manufacturing facility could disrupt our business and adversely affect our operations.

Our principal operations are located in Northern California, including our corporate headquarters and manufacturing facility in Berkeley, California. This location is in an area of seismic activity near active earthquake faults. Any earthquake, terrorist attack, fire, power shortage or other calamity affecting our facilities may disrupt our business and could have material adverse effect on our business and results of operations.

We have a significant stockholder, which may limit other stockholders’ ability to influence corporate matters and may give rise to conflicts of interest.

Entities controlled by Felix J. Baker and Julian C. Baker beneficially own approximately 30.5% of our outstanding common stock as of August 3, 2012, which includes warrants to purchase approximately 7.6 million shares of XOMA’s common stock at an exercise price of $1.76 per share. On July 19, 2012, our Board of Directors elected Kelvin Neu, M.D., to serve on our Board of Directors. Dr. Neu is a Managing Director at Baker Bros. Advisors, LLC, an entity controlled by Felix J. Baker and Julian C. Baker. Accordingly, these entities may exert significant influence over us and any action requiring the approval of the holders of our stock, including the election of directors and approval of significant corporate transactions. Furthermore, conflicts of interest could arise in the future between us, on the one hand, and these entities, on the other hand, concerning potential competitive business activities, business opportunities, the issuance of additional securities and other matters.

Our shareholder rights agreement and organizational documents contain provisions that may prevent transactions that could be beneficial to our stockholders and may insulate our management from removal.

In February 2003, we adopted a new shareholder rights agreement (to replace the shareholder rights agreement that had expired), which could make it considerably more difficult or costly for a person or group to acquire control of us in a transaction that our Board of Directors opposes.

Our charter and by-laws:

require certain procedures to be followed and time periods to be met for any stockholder to propose matters to be considered at annual meetings of stockholders, including nominating directors for election at those meetings; and

authorize our Board of Directors to issue up to 1,000,000 shares of preferred stock without stockholder approval and to set the rights, preferences and other designations, including voting rights, of those shares as the Board of Directors may determine.

In addition, we are subject to the provisions of Section 203 of the Delaware General Corporation Law (the “DGCL”), that may prohibit large stockholders, in particular those owning 15% or more of our outstanding common stock, from merging or combining with us.

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These provisions of our shareholder rights agreement, our organizational documents and the DGCL, alone or in combination with each other, may discourage transactions involving actual or potential changes of control, including transactions that otherwise could involve payment of a premium over prevailing market prices to holders of common stock, could limit the ability of stockholders to approve transactions that they may deem to be in their best interests, and could make it considerably more difficult for a potential acquirer to replace management.

Risks Relating to our Common Stock and this Offering

You will experience immediate and substantial dilution in the net tangible book value per share of the common stock you purchase and may also experience further dilution.

Since the price per share of our common stock being offered is substantially higher than the net tangible book value per share of our common stock, you will suffer substantial dilution in the net tangible book value of the common stock you purchase in this offering. Based on the public offering price of $3.00 per share, if you purchase common stock in this offering, you will suffer immediate and substantial dilution of $2.50 per share in the net tangible book value of the common stock. See “Dilution” below for a more detailed discussion of the dilution you will incur if you purchase common stock in this offering.

To the extent that outstanding options or warrants are exercised or restricted stock units vest, you will experience further dilution. As of June 30, 2012, there were 5,709,599 stock options outstanding, with a weighted average exercise price of $10.18 per share, 1,387,048 restricted stock units outstanding, and warrants outstanding to purchase 347,826 shares of common stock at an exercise price of $19.50 per share, 1,260,000 shares of common stock at an exercise price of $10.50 per share, 14,829,167 shares of common stock at an exercise price of $1.76 per share, and 263,158 shares of common stock at an exercise price of $1.14 per share.

In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders.

We may issue additional equity securities and thereby materially and adversely affect the price of our common stock.

We are authorized to issue, without stockholder approval, 1,000,000 shares of preferred stock, of which none were issued and outstanding as of August 3, 2012, which may give other stockholders dividend, conversion, voting, and liquidation rights, among other rights, which may be superior to the rights of holders of our common stock. In April 2011, the 2,959 Series B convertible preference shares previously issued to Genentech were converted by Genentech into 254,560 shares of common stock. In addition, we are authorized to issue, generally without stockholder approval, up to 138,666,666 shares of common stock, of which 68,192,351 were issued and outstanding as of August 3, 2012. If we issue additional equity securities, the price of our common stock may be materially and adversely affected.

On February 4, 2011, we entered into an At Market Issuance Sales Agreement (the “2011 ATM Agreement”) with McNicoll, Lewis & Vlak LLC (now known as MLV & Co. LLC, “MLV”), under which we may sell shares of our common stock from time to time through the MLV, as our agent for the offer and sale of the shares, in an aggregate amount not to exceed the amount that can be sold under our Registration Statement on Form S-3 (File No. 333-172197) filed with the SEC on February 11, 2011 and amended on March 10, 2011, June 3, 2011 and January 3, 2012, which was most recently declared effective by the SEC on January 17, 2012. MLV may sell the shares by any method permitted by law deemed to be an “at the market” offering as defined in Rule 415 of the Securities Act of 1933, as amended (the “Securities Act”), including without limitation sales made directly on The NASDAQ Global Market, on any other existing trading market for our common stock or to or through a market maker. MLV may also sell the shares in privately negotiated transactions, subject to our prior approval. From the inception of the 2011 ATM Agreement through August 3, 2012, we sold a total of 7,572,327 shares of common stock under this agreement for aggregate gross proceeds of $14.6 million.

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On March 9, 2012, we completed an underwritten public offering of 29,669,154 shares of our common stock, and accompanying warrants to purchase one half of a share of common stock for each share purchased, at a public offering price of $1.32 per share. Total gross proceeds from the offering were approximately $39.2 million, before deducting underwriting discounts and commissions and estimated offering expenses totaling approximately $3.0 million. The warrants, which represent the right to acquire an aggregate of up to 14,834,577 shares of common stock, are immediately exercisable and have a five-year term and an exercise price of $1.76 per share.

In addition, funding from collaboration partners and others has in the past and may in the future involve issuance by us of our shares of common stock. We cannot be certain how the purchase price of such shares, the relevant market price or premium, if any, will be determined or when such determinations will be made. Any such issuance could result in dilution in the value of our issued and outstanding shares.

Our share price may be volatile and there may not be an active trading market for our common stock.

There can be no assurance that the market price of our common stock will not decline below its present market price or that there will be an active trading market for our common stock. The market prices of biotechnology companies have been and are likely to continue to be highly volatile. Fluctuations in our operating results and general market conditions for biotechnology stocks could have a significant impact on the volatility of our common stock price. We have experienced significant volatility in the price of our common stock. From January 1, 2011 through October 23, 2012, the share price of our common stock has ranged from a high of $7.71 to a low of $1.04. Factors contributing to such volatility include, but are not limited to:

results of preclinical studies and clinical trials;

information relating to the safety or efficacy of products or product candidates;

developments regarding regulatory filings;

announcements of new collaborations;

failure to enter into collaborations;

developments in existing collaborations;

our funding requirements and the terms of our financing arrangements;

technological innovations or new indications for our therapeutic products and product candidates;

introduction of new products or technologies by us or our competitors;

sales and estimated or forecasted sales of products for which we receive royalties, if any;

government regulations;

developments in patent or other proprietary rights;

the number of shares issued and outstanding;

the number of shares trading on an average trading day;

announcements regarding other participants in the biotechnology and pharmaceutical industries; and

market speculation regarding any of the foregoing.

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If we are unable to continue to meet the requirements for continued listing on The NASDAQ Global Market, then we may be de-listed. In March 2010, we received a Staff Determination letter from The NASDAQ Stock Market LLC indicating we had not regained compliance with the minimum $1.00 per share requirement for continued inclusion on The NASDAQ Global Market, pursuant to NASDAQ Listing Rule 5450(a)(1). On August 18, 2010, we effected a 1-for-15 reverse split of our common stock to regain compliance.

Management will have broad discretion in determining how to use the proceeds of this offering.

We have not determined the amounts we plan to spend on any of the areas listed in “Use of Proceeds” below or the timing of such expenditures. Accordingly, the amount and timing of our actual expenditures will depend on numerous factors, including the progress of our research and development activities and clinical trials and the amount of cash generated by our operations. As a result, our management will have broad discretion to allocate the net proceeds from this offering, and may spend the proceeds in ways with which our stockholders may not agree. Pending application of the net proceeds as described in “Use of Proceeds”, we intend to invest the net proceeds of the offering in short-term, interest-bearing securities, investment grade securities, certificates of deposit or direct or guaranteed obligations of the U.S. government. These investments may not yield a favorable return to our stockholders.

A substantial number of shares of our common stock may be sold in this offering, which could cause the price of our common stock to decline.

In this offering we will sell 13,333,333 shares, or approximately 19.6% of our outstanding common stock as of June 30, 2012. This sale and any future sales of a substantial number of shares of our common stock in the public market, or the perception that such sales may occur, could adversely affect the price of our common stock. We cannot predict the effect, if any, that market sales of those shares of common stock or the availability of those shares of common stock for sale will have on the market price of our common stock.

FORWARD-LOOKING INFORMATION

Certain statements contained in this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference therein, related to the anticipated size of clinical trials, the anticipated timing of initiation of clinical trials, the expected availability of clinical trial results, the sufficiency of our cash resources, the estimated costs of clinical trials and the amounts of certain revenues and certain costs in comparison to prior years, or that otherwise relate to future periods, are forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). The words “believe,” “may,” “estimate,” “continue,” “anticipate,” “intend,” “expect,” “predict,” “potential” and similar expressions are intended to identify forward-looking statements. These statements are based on assumptions that may not prove accurate. Actual results could differ materially from those anticipated due to certain risks inherent in the biotechnology industry and for companies engaged in the development of new products in a regulated market. Among other things: our product candidates are still being developed, and we will require substantial funds to continue development which may not be available; we have sustained losses in the past and we expect to sustain losses in the future; we are substantially dependent on Servier for the development and commercialization of gevokizumab and for other aspects of our business; we have received negative results from certain of our clinical trials, and we face uncertain results of other clinical trials of our product candidates; if our therapeutic product candidates do not receive regulatory approval, neither our third-party collaborators, our contract manufacturers nor we will be able to manufacture and market them; we may not obtain orphan drug exclusivity or we may not receive the full benefit of orphan drug exclusivity even if we obtain such exclusivity; even once approved, a product may be subject to additional testing or significant marketing restrictions, its approval may be withdrawn or it may be voluntarily taken off the market; we may not be successful in commercializing our products, which could also affect our development efforts; we are subject to various state and federal healthcare related laws and regulations that may impact the commercialization of ACEON or our product candidates and could subject us to significant fines and penalties; and certain of our technologies are in-licensed from third parties, so our capabilities using them are restricted and subject to additional risks. These and other risks, including those related to current economic and financial market conditions, are described in more detail in “Risk Factors” above and the additional risk factors contained in our most recent Annual Report on Form 10-K and Quarterly Reports on Form 10-Q. We undertake no obligation to publicly update any forward-looking statements, regardless of any new information, future events or other occurrences. We advise you, however, to consult any additional disclosures we make in our reports to the SEC on Forms 10-K, 10-Q and 8-K.

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USE OF PROCEEDS

We estimate the net proceeds from this offering will be approximately $36.9 million, after deducting underwriting discounts and commissions and our estimated offering expenses.

We currently intend to use the net proceeds from this offering for continued development, preclinical testing and clinical studies related to gevokizumab and our XMet platform, including the design and conduct of two pivotal Phase 3 clinical studies to evaluate gevokizumab for the treatment of Schnitzler syndrome and Neutrophilic Dermatoses, preclinical testing and development of XMetA and XMetS to enhance their licensable value, and development work on XMetD to prepare the product candidate for clinical studies. Although many of these activities are in early planning stages and therefore are subject to change, we currently estimate expenditures for these activities to be approximately $15 million. We intend to use the remainder of the net proceeds for general research and development, business development and other corporate purposes as determined by our management.

While we have estimated the particular uses for the net proceeds of this offering, the amount and timing of our actual expenditures will depend on numerous factors, including the progress of our research and development activities and clinical trials and the amount of cash generated by our operations.

As a result, our management will retain broad discretion in the allocation and use of the net proceeds of this offering, and investors will be relying on the judgment of our management with regard to the use of these net proceeds. Pending application of the net proceeds for the specified purposes as described above, we expect to invest the net proceeds in short-term, interest-bearing securities, investment grade securities, certificates of deposit or direct or guaranteed obligations of the U.S. government.

DILUTION

Our net tangible book value as of June 30, 2012, was approximately $3.9 million, or $0.06 per share of common stock. Net tangible book value per share is determined by dividing our total tangible assets, less total liabilities, by the number of our shares of common stock outstanding as of June 30, 2012. Dilution in net tangible book value per share represents the difference between the amount per share paid by purchasers of common stock in this offering and the net tangible book value per share of our common stock immediately after this offering.

After giving effect to the sale of 13,333,333 shares of common stock in this offering at the public offering price of $3.00 per share, and after deducting the underwriting discounts and commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of June 30, 2012, would have been approximately $40.8 million, or $0.50 per share. This represents an immediate increase in net tangible book value of $0.44 per share to existing stockholders and immediate dilution in net tangible book value of $2.50 per share to new investors purchasing our shares of common stock in this offering. The following table illustrates this dilution on a per share basis:

Public offering price per share			$	3.00
Net tangible book value per share as of June 30, 2012	$	0.06
Increase per share attributable to investors participating in this offering	$	0.44

As adjusted net tangible book value per share after this offering			$	0.50
Dilution per share to investors participating in this offering			$	2.50

The foregoing table does not take into account further dilution to new investors that could occur upon the exercise of outstanding options and warrants having a per share exercise price less than the per share offering price to the public in this offering or upon the vesting of outstanding restricted stock units.

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The above discussion and table are based on 68,107,116 shares of common stock outstanding as of June 30, 2012, and exclude:

shares of common stock issuable upon the vesting of outstanding restricted stock units, of which there were 1,387,048 outstanding as of June 30, 2012;

UNDERWRITING

Under the terms and subject to the conditions contained in an underwriting agreement dated the date of this prospectus supplement, we have agreed to sell to the underwriters named below, for whom Credit Suisse Securities (USA) LLC and Cowen and Company, LLC are acting as representatives, the following respective numbers of shares of common stock:

Underwriter	Number of Shares
Credit Suisse Securities (USA) LLC		8,000,000
Cowen and Company, LLC		5,333,333

Total		13,333,333

The underwriting agreement provides that the underwriters are obligated to purchase all the shares of common stock in the offering if any are purchased, other than those shares covered by the over-allotment option described below. The underwriting agreement also provides that if an underwriter defaults the purchase commitments of non-defaulting underwriters may be increased or the offering may be terminated.

We have granted to the underwriters a 30-day option to purchase on a pro rata basis up to 1,999,999 additional shares at the initial public offering price less the underwriting discounts and commissions. The option may be exercised only to cover any over-allotments of common stock.

The underwriters are offering the shares, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel including the validity of the shares, and subject to other conditions contained in the underwriting agreement, such as the receipt by the underwriters of officer’s certificates and legal opinions. The offering of the shares by the underwriters is also subject to the underwriters’ right to reject any order in whole or in part.

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The underwriters propose to offer the shares of common stock initially at the public offering price on the cover page of this prospectus supplement and to selling group members at that price less a selling concession of up to $0.108 per share. After the initial public offering the representatives may change the public offering price and concession.

The following table summarizes the per share and total underwriting discounts and commissions to be paid to the underwriters assuming both no exercise and full exercise of the underwriters’ option to purchase up to 1,999,999 additional shares:

	Per Share				Total
	Without Over-allotment		With Over-allotment		Without Over-allotment		With Over-allotment
Underwriting Discounts and Commissions paid by us	$	0.18	$	0.18	$	2,400,000	$	2,760,000

We estimate our out of pocket expenses for this offering (not including any underwriting discounts and commissions) will be approximately $675,000, which includes up to $150,000 that we have agreed to reimburse the underwriters for their legal fees and certain other expenses incurred by them in connection with this offering and a fee of $200,000 that we have agreed to pay to Wedbush Securities for certain financial advisory services in connection with this offering.

We have agreed we will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, or file with the SEC a registration statement under the Securities Act relating to, any shares of our common stock or securities convertible into or exchangeable or exercisable for any shares of our common stock, or publicly disclose the intention to make any offer, sale, pledge, disposition or filing, without the prior written consent of Credit Suisse Securities (USA) LLC and Cowen and Company, LLC for a period of 90 days after the date of this prospectus supplement. The restrictions described in this paragraph do not apply to awards by us to purchase, or issuance by us of, shares of common stock pursuant to employee benefit plans existing on, or upon the exercise, conversion or exchange of convertible or exchangeable securities outstanding as of, the date of this prospectus supplement. In addition, these restrictions do not prevent us from issuing shares of our common stock as consideration in connection with collaborations, acquisitions or strategic transactions approved by a majority of our disinterested directors, subject to certain limitations, provided that the total number of shares issued does not exceed 5% of the outstanding shares of our common stock as of the date of the underwriting agreement. However, in the event that either (1) during the last 17 days of the “lock-up” period, we release earnings results or material news or a material event relating to us occurs or (2) prior to the expiration of the ‘lock-up’ period, we announce that we will release earnings results during the 16-day period beginning on the last day of the ‘lock-up’ period, then in either case the expiration of the ‘lock-up” will be extended until the expiration of the 18-day period beginning on the date of the release of the earnings results or the occurrence of the material news or event, as applicable, unless Credit Suisse Securities (USA) LLC and Cowen and Company, LLC waive, in writing, such an extension.

Our officers and directors have agreed they will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, any shares of our common stock or securities convertible into or exchangeable or exercisable for any shares of our common stock, enter into a transaction that would have the same effect, or enter into any swap, hedge or other arrangement that transfers, in whole or in part, any of the economic consequences of ownership of our common stock, whether any of these transactions are to be settled by delivery of our common stock or other securities, in cash or otherwise, or publicly disclose the intention to make any offer, sale, pledge or disposition, or to enter into any transaction, swap, hedge or other arrangement, without, in each case, the prior written consent of Credit Suisse Securities (USA) LLC and Cowen and Company, LLC, for a period of 90 days after the date of this prospectus supplement. The restrictions described in this paragraph do not apply to, subject to certain conditions, transfers of shares (i) as a bona fide gift or gifts or pledge, (ii) to an immediate family member of such person or to a trust, the beneficiaries of which are exclusively such person and one or more immediate family members, (iii) with the prior written consent of Credit Suisse Securities (USA) LLC and Cowen and Company, LLC, (iv) in connection with the exercise of any equity award granted to them that expires or is otherwise required to be exercised during the 90 day period to discharge tax obligations resulting from such exercise, or (v) to us to discharge tax withholding obligations resulting from the vesting or release of equity awards. However, in the event that either (1) during the last 17 days of the ‘lock-up” period, we release earnings results or material news or a material event relating to us occurs or (2) prior to the expiration of the “lock-up” period, we announce that we will release earnings results during the 16-day period beginning on the last day of the “lock-up” period, then in either case the expiration of the “lock-up” will be extended until the expiration of the 18-day period beginning on the date of the release of the earnings results or the occurrence of the material news or event, as applicable, unless Credit Suisse Securities (USA) LLC and Cowen and Company, LLC waive, in writing, such an extension.

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We have agreed to indemnify the underwriters against liabilities under the Securities Act, or contribute to payments that the underwriters may be required to make in that respect.

Our common stock is listed on The NASDAQ Global Market under the symbol “XOMA.”

In connection with the offering the underwriters may engage in stabilizing transactions, over-allotment transactions, syndicate covering transactions, penalty bids and passive market making in accordance with Regulation M under the Exchange Act.

Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum.

Over-allotment involves sales by the underwriters of shares in excess of the number of shares the underwriters are obligated to purchase, which creates a syndicate short position. The short position may be either a covered short position or a naked short position. In a covered short position, the number of shares over-allotted by the underwriters is not greater than the number of shares that they may purchase in the over-allotment option. In a naked short position, the number of shares involved is greater than the number of shares in the over-allotment option. The underwriters may close out any covered short position by either exercising their over-allotment option and/or purchasing shares in the open market.

Syndicate covering transactions involve purchases of the common stock in the open market after the distribution has been completed in order to cover syndicate short positions. In determining the source of shares to close out the short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the over-allotment option. If the underwriters sell more shares than could be covered by the over-allotment option, a naked short position, the position can only be closed out by buying shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there could be downward pressure on the price of the shares in the open market after pricing that could adversely affect investors who purchase in the offering.

Penalty bids permit the representatives to reclaim a selling concession from a syndicate member when the common stock originally sold by the syndicate member is purchased in a stabilizing or syndicate covering transaction to cover syndicate short positions.

In passive market making, market makers in the common stock who are underwriters or prospective underwriters may, subject to limitations, make bids for or purchases of our common stock until the time, if any, at which a stabilizing bid is made.

These stabilizing transactions, syndicate covering transactions and penalty bids may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of the common stock. As a result the price of our common stock may be higher than the price that might otherwise exist in the open market. These transactions may be effected on The NASDAQ Global Market or otherwise and, if commenced, may be discontinued at any time.

This prospectus supplement and accompanying prospectus in electronic format may be made available on the web sites maintained by one or more of the underwriters, or selling group members, if any, participating in this offering and one or more of the underwriters participating in this offering may distribute this prospectus supplement and accompanying prospectus electronically. The representatives may agree to allocate a number of shares to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the underwriters and selling group members that will make internet distributions on the same basis as other allocations.

From time to time in the ordinary course of their respective businesses, certain of the underwriters and their affiliates have performed and may in the future perform investment banking, commercial banking, dealer and advisory services for us or our affiliates for which they have received or will receive customary fees and expenses.

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Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area that has implemented the Prospectus Directive (each, a “Relevant Member State”), an offer to the public of any shares that are the subject of the offering contemplated by this prospectus supplement (the “Shares”) may not be made in that Relevant Member State, except that an offer to the public in that Relevant Member State of any Shares may be made at any time under the following exemptions under the Prospectus Directive, if they have been implemented in that Relevant Member State:

(a)

to any legal entity that is a qualified investor as defined in the Prospectus Directive;

(b)

to fewer than 100 or, if the Relevant Member State has implemented the relevant provision of the 2010 PD Amending Directive, 150 natural or legal persons (other than qualified investors as defined in the Prospectus Directive), as permitted under the Prospectus Directive, subject to obtaining the prior consent of the representative for any such offer; or

(c)

in any other circumstances falling within Article 3(2) of the Prospectus Directive,

provided that no such offer of Shares shall require the publication by us or any underwriter of a prospectus pursuant to Article 3 of the Prospectus Directive.

For the purposes of this provision, the expression an “offer to the public” in relation to any Shares in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and any Shares to be offered so as to enable an investor to decide to purchase any Shares, as the same may be varied in that Member State by any measure implementing the Prospectus Directive in that Member State, the expression “Prospectus Directive” means Directive 2003/71/EC (and amendments thereto, including the 2010 PD Amending Directive, to the extent implemented in the Relevant Member State), and includes any relevant implementing measure in the Relevant Member State, and the expression “2010 PD Amending Directive” means Directive 2010/73/EU.

Notice to Prospective Investors in the United Kingdom

Each underwriter has severally represented and agreed that:

(a)

it has only communicated or caused to be communicated and will only communicate or cause to be communicated an invitation or inducement to engage in investment activity (within the meaning of Section 21 of the Financial Services and Markets Act, or the FSMA) received by it in connection with the issue or sale of the shares in circumstances in which Section 21(1) of the FSMA does not apply to us; and

(b)

it has complied and will comply with all applicable provisions of the FSMA with respect to anything done by it in relation to the shares in, from or otherwise involving the United Kingdom.

NOTICE TO CANADIAN RESIDENTS

Resale Restrictions

The distribution of the shares of common stock in Canada is being made only in the provinces of Ontario, Quebec, Alberta, British Columbia and Manitoba on a private placement basis exempt from the requirement that we prepare and file a prospectus with the securities regulatory authorities in each province where trades of the shares of common stock are made. Any resale of the shares of common stock in Canada must be made under applicable securities laws which may vary depending on the relevant jurisdiction, and which may require resales to be made under available statutory exemptions or under a discretionary exemption granted by the applicable Canadian securities regulatory authority. Purchasers are advised to seek legal advice prior to any resale of the shares of common stock.

Representations of Purchasers

By purchasing shares of common stock in Canada and accepting delivery of a purchase confirmation, a purchaser is representing to us and the dealer from whom the purchase confirmation is received that:

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the purchaser is entitled under applicable provincial securities laws to purchase the shares of common stock without the benefit of a prospectus qualified under those securities laws as it is an “accredited investor” as defined under National Instrument 45-106 – Prospectus and Registration Exemptions;

the purchaser is a “Canadian permitted client” as defined in National Instrument 31-103 - Registration Requirements and Exemptions, or as otherwise interpreted and applied by the Canadian Securities Administrators,

where required by law, the purchaser is purchasing as principal and not as agent;

the purchaser has reviewed the text above under Resale Restrictions; and

the purchaser acknowledges and consents to the provision of specified information concerning the purchase of the shares of common stock to the regulatory authority that by law is entitled to collect the information, including certain personal information. For purchasers in Ontario, questions about such indirect collection of personal information should be directed to Administrative Support Clerk, Ontario Securities Commission, Suite 1903, Box 55, 20 Queen Street West, Toronto, Ontario M5H 3S8 or on (416) 593-3684.

Rights of Action – Ontario Purchasers

Under Ontario securities legislation, certain purchasers who purchase a security offered by this prospectus supplement and accompanying prospectus during the period of distribution will have a statutory right of action for damages, or while still the owner of the shares of common stock, for rescission against us in the event that this prospectus supplement and accompanying prospectus contain a misrepresentation without regard to whether the purchaser relied on the misrepresentation. The right of action for damages is exercisable not later than the earlier of 180 days from the date the purchaser first had knowledge of the facts giving rise to the cause of action and three years from the date on which payment is made for the shares of common stock. The right of action for rescission is exercisable not later than 180 days from the date on which payment is made for the shares of common stock. If a purchaser elects to exercise the right of action for rescission, the purchaser will have no right of action for damages against us. In no case will the amount recoverable in any action exceed the price at which the shares of common stock were offered to the purchaser and if the purchaser is shown to have purchased the securities with knowledge of the misrepresentation, we will have no liability. In the case of an action for damages, we will not be liable for all or any portion of the damages that are proven to not represent the depreciation in value of the shares of common stock as a result of the misrepresentation relied upon. These rights are in addition to, and without derogation from, any other rights or remedies available at law to an Ontario purchaser. The foregoing is a summary of the rights available to an Ontario purchaser. Ontario purchasers should refer to the complete text of the relevant statutory provisions.

Enforcement of Legal Rights

All of our directors and officers as well as the experts named herein may be located outside of Canada and, as a result, it may not be possible for Canadian purchasers to effect service of process within Canada upon us or those persons. All or a substantial portion of our assets and the assets of those persons may be located outside of Canada and, as a result, it may not be possible to satisfy a judgment against us or those persons in Canada or to enforce a judgment obtained in Canadian courts against us or those persons outside of Canada.

Taxation and Eligibility for Investment

Canadian purchasers of shares of common stock should consult their own legal and tax advisors with respect to the tax consequences of an investment in the shares of common stock in their particular circumstances and about the eligibility of the shares of common stock for investment by the purchaser under relevant Canadian legislation.

LEGAL MATTERS

Certain legal matters with respect to the legality of the issuance of the shares of common stock offered by us will be passed upon for us by Cooley LLP, Palo Alto, California. The underwriters are being represented by Latham & Watkins LLP, Menlo Park, California in connection with this offering.

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EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2011, and the effectiveness of our internal control over financial reporting as of December 31, 2011, as set forth in their reports, which are incorporated by reference in this prospectus supplement and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s reports, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We are subject to the reporting requirements of the Exchange Act and file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy these reports, proxy statements and other information at the SEC’s public reference facilities at 100 F Street, N.E., Room 1580, Washington, D.C. 20549. You can request copies of these documents by writing to the SEC and paying a fee for the copying cost. Please call the SEC at 1-800-SEC-0330 for more information about the operation of the public reference facilities. SEC filings are also available at the SEC’s website at http://www.sec.gov. Our common stock is listed on The NASDAQ Global Market, and you can read and inspect our filings at the offices of The NASDAQ Stock Market at 1735 K Street, Washington, D.C. 20006.

This prospectus supplement and the accompanying prospectus are only part of a registration statement on Form S-3 that we have filed with the SEC under the Securities Act and therefore omit certain information contained in the registration statement. We have also filed exhibits and schedules with the registration statement that are excluded from this prospectus supplement and the accompanying prospectus, and you should refer to the applicable exhibit or schedule for a complete description of any statement referring to any contract or other document. You may inspect a copy of the registration statement, including the exhibits and schedules, without charge, at the public reference room or obtain a copy from the SEC upon payment of the fees prescribed by the SEC.

We also maintain a website at http://www.xoma.com, through which you can access our SEC filings. The information set forth on our website is not part of this prospectus supplement.

INCORPORATION OF DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” the information we file with the SEC. This permits us to disclose important information to you by referring to these filed documents. Any information referred to in this way is considered part of this prospectus supplement. The information incorporated by reference is an important part of this prospectus supplement and the accompanying prospectus, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the following documents that have been filed with the SEC (other than information furnished under Item 2.02 or Item 7.01 of Form 8-K and all exhibits related to such items):

our annual report on Form 10-K for the year ended December 31, 2011, filed with the SEC on March 14, 2012, including the information specifically incorporated by reference therein from our definitive proxy statement on Schedule 14A, filed on April 11, 2012;

our quarterly reports on Form 10-Q for the fiscal quarters ended March 31, 2012, and June 30, 2012, filed with the SEC on May 8, 2012, and August 7, 2012, respectively;

our current reports on Form 8-K, filed with the SEC on January 6, 2012, January 17, 2012, February 14, 2012, March 7, 2012, May 31, 2012, July 13, 2012, July 23, 2012, October 3, 2012, October 23, 2012, and October 24, 2012; and

the description of our capital stock included under the caption “Description of Capital Stock” in the prospectus dated December 16, 2011, which was filed on December 19, 2011, and is part of our registration statement on Form S-4/A filed on December 13, 2011 (registration no. 333-177165), including any amendment or report for the purpose of updating such description.

S -36

Any information in any of the foregoing documents will automatically be deemed to be modified or superseded to the extent that information in this prospectus supplement and the accompanying prospectus or in a later filed document that is incorporated or deemed to be incorporated herein by reference modifies or replaces such information.

We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus supplement and prior to the termination of the offering of the securities made by this prospectus supplement and the accompanying prospectus. Information in such future filings updates and supplements the information provided in this prospectus supplement and the accompanying prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

We will provide, upon written or oral request, without charge to each person, including any beneficial owner, to whom a copy of this prospectus supplement and the accompanying prospectus is delivered, a copy of any or all of the information incorporated herein by reference (exclusive of exhibits to such documents unless such exhibits are specifically incorporated by reference herein). You may request in writing or orally a copy of these filings, at no cost, by writing or telephoning us at the following address:

XOMA Corporation

2910 Seventh Street

Berkeley, California 94710

(510) 204-7200

S -37

Prospectus

$100,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

From time to time, we may offer and sell any combination of the securities described in this prospectus, either individually or in combination, for total gross proceeds of up to $100,000,000. We may also offer common stock or preferred stock upon conversion of debt securities, common stock upon conversion of preferred stock, or common stock, preferred stock or debt securities upon the exercise of warrants.

We will provide the specific terms of these offerings and securities in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectus, as well as any documents incorporated by reference, before buying any of the securities being offered.

Our common stock is listed on The NASDAQ Global Market under the trading symbol “XOMA.” On August 21, 2012, the last reported sale price of our common stock was $3.17 per share. The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on The NASDAQ Global Market or other securities exchange of the securities covered by the prospectus supplement.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the other documents that are incorporated by reference into this prospectus.

This prospectus may not be used to consummate a sale of securities unless accompanied by a prospectus supplement.

The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. The supplements to this prospectus will provide the specific terms of the plan of distribution. If any agents or underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents or underwriters and any applicable fees, commissions, discounts and over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds that we expect to receive from such sale will also be set forth in a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is September 7, 2012.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS		i
PROSPECTUS SUMMARY		1
RISK FACTORS		5
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		5
USE OF PROCEEDS		7
RATIO OF EARNINGS TO FIXED CHARGES		7
DESCRIPTION OF CAPITAL STOCK		7
DESCRIPTION OF DEBT SECURITIES		12
DESCRIPTION OF WARRANTS		18
LEGAL OWNERSHIP OF SECURITIES		20
PLAN OF DISTRIBUTION		23
LEGAL MATTERS		24
EXPERTS		24
WHERE YOU CAN FIND MORE INFORMATION		24
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		25

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may offer and sell, either individually or in combination, in one or more offerings, any combination of the securities described in this prospectus, for total gross proceeds of up to $100,000,000. This prospectus provides you with a general description of the securities we may offer.

Each time we offer securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents that we have incorporated by reference into this prospectus. We urge you to read carefully this prospectus, any applicable prospectus supplement and any free writing prospectuses we have authorized for use in connection with a specific offering, together with the information incorporated herein by reference as described under the heading “Incorporation of Certain Information by Reference,” before buying any of the securities being offered.

This prospectus may not be used to consummate a sale of securities unless it is accompanied by a prospectus supplement.

You should rely only on the information contained in, or incorporated by reference into, this prospectus and any applicable prospectus supplement, along with the information contained in any free writing prospectuses we have authorized for use in connection with a specific offering. We have not authorized anyone to provide you with different or additional information. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so.

The information appearing in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate only as of the date on the front of the document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus, any applicable prospectus supplement or any related free writing prospectus, or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the section entitled “Where You Can Find More Information.”

This prospectus contains and incorporates by reference, and any prospectus supplement or free writing prospectus may contain and incorporate by reference, market data and industry statistics and forecasts that are based on independent industry publications and other publicly available information. Although we believe these sources are reliable, we do not guarantee the accuracy or completeness of this information and we have not independently verified this information. Although we are not aware of any misstatements regarding the market and industry data presented in this prospectus and the documents incorporated herein by reference, these estimates involve risks and uncertainties and are subject to change based on various factors, including those discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. Accordingly, investors should not place undue reliance on this information.

This prospectus and the information incorporated herein by reference include trademarks, service marks and trade names owned by us or other companies. All trademarks, service marks and trade names included or incorporated by reference into this prospectus, any applicable prospectus supplement or any related free writing prospectus are the property of their respective owners.

PROSPECTUS SUMMARY

This summary highlights selected information contained elsewhere in this prospectus or incorporated by reference in this prospectus, and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectus, including the risks of investing in our securities discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus is a part.

References in this prospectus to “XOMA”, “the Company,” “we”, “us” and “our” refer to XOMA Corporation, a Delaware corporation, and its consolidated subsidiaries, if any, unless otherwise specified.

XOMA CORPORATION

Overview

We are a leader in the discovery and development of innovative antibody-based therapeutics. Our lead drug candidate is gevokizumab (formerly XOMA 052), a humanized antibody designed to inhibit the pro-inflammatory cytokine interleukin-1 beta, or IL-1 beta, which is believed to be a primary trigger of pathologic inflammation in multiple diseases. We have entered into a license and collaboration agreement with Les Laboratoires Servier, or Servier, to jointly develop and commercialize gevokizumab in multiple indications. In collaboration with our partner, Servier, we initiated patient enrollment in June 2012 in a global Phase 3 clinical study investigating the ability of gevokizumab to reduce the signs and symptoms, including vitreous haze, in patients with non-infectious uveitis, or NIU, and Behçet’s uveitis. We anticipate that Servier will launch a Phase 2 proof-of-concept study for gevokizumab in a cardiovascular disease indication during the second half of 2012. Separately, we have launched a Phase 2 proof-of-concept program for gevokizumab to evaluate additional indications, including a clinical trial in moderate-to-severe inflammatory acne, for which we initiated patient enrollment in December 2011, and a clinical trial in erosive osteoarthritis, or EOA, of the hand, for which we initiated patient enrollment in June 2012.

Our proprietary preclinical pipeline includes classes of antibodies that activate or sensitize the insulin receptor in vivo and represent potential new therapeutic approaches to the treatment of diabetes. We have developed these and other antibodies using some or all of our ADAPT™ antibody discovery and development platform, our ModulX™ technologies for generating allosterically modulating antibodies, and our OptimX™ technologies for optimizing biophysical properties of antibodies, including affinity, immunogenicity, stability and manufacturability.

In January 2012, we announced that we had acquired certain U.S. rights to a portfolio of antihypertensive products from Servier. The portfolio includes ACEON ® (perindopril erbumine), a currently marketed angiotensin converting enzyme, or ACE, inhibitor, and three fixed-dose combination, or FDC, product candidates where perindopril is combined with another active ingredient(s), such as a calcium channel blocker. The proprietary form of perindopril in each of the combination product candidates provides patent protection until April 2023. We assumed commercialization activities for ACEON in January 2012 following the transfer from Servier’s previous licensee. In late February 2012, we initiated enrollment in a Phase 3 trial for perindopril arginine and amlodipine besylate, the first FDC product candidate, or FDC1. Based on regulatory interaction to date, if the trial generates positive results, we expect it to be the only efficacy trial needed to complement existing clinical data and that it will support the submission of an application to the FDA seeking approval for FDC1. Partial funding for the Phase 3 trial has been provided by Servier; the balance of study expenses, consisting primarily of costs generated by our contract research organization, we expect to pay over time from the profits generated by our ACEON sales. We will not create a primary care sales force to market the FDC product candidates as we believe these can be successfully promoted by a third party with an existing sales force or under some alternate approach.

Our biodefense initiatives currently include a $65.0 million multiple-year contract funded by the National Institute of Allergy and Infectious Diseases, or NIAID, a part of the National Institutes of Health, or NIH, to support our ongoing development of anti-botulism antibody product candidates, of which the first, XOMA 3AB, is in a Phase 1 clinical trial. This contract is the third that NIAID has awarded us for the development of botulinum antitoxins. In October 2011, we announced that we had been awarded a fourth contract for up to $28.0 million over five years to develop broad-spectrum antitoxins for the treatment of human botulism poisoning, bringing the program’s total potential awards to approximately $120 million. In January 2012, we announced that we will complete the NIAID biodefense contracts currently in place but will not actively pursue future contracts. Should the U.S. government choose to acquire XOMA 3AB or other biodefense products in the future, we expect to be able to provide these antibodies through an outside manufacturer.

We also have developed antibody product candidates with premier pharmaceutical companies including Novartis AG, or Novartis, and Takeda Pharmaceutical Company Limited, or Takeda. Two antibodies developed with Novartis, LFA102 and HCD122 (lucatumumab), are in Phase 1 and/or Phase 2 clinical development by Novartis for the potential treatment of breast or prostate cancer and hematological malignancies, respectively.

Risks Associated with our Business

Our business is subject to numerous risks, as described under the heading “Risk Factors” contained in the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the documents that are incorporated by reference into this prospectus.

Company Information

We were incorporated in Delaware in 1981 and became a Bermuda exempted company in December 1998. Effective December 31, 2011, we changed our jurisdiction of incorporation from Bermuda to Delaware and changed our name from XOMA Ltd. to XOMA Corporation.

Our principal executive offices are located at 2910 Seventh Street, Berkeley, California 94710, and we maintain a registered office located at Corporation Trust Center, 1209 Orange Street, Wilmington, Delaware 19801. Our telephone number at our principal executive offices is (510) 204-7200. Our website address is www.xoma.com. Information found on, or accessible through, our website is not a part of, and is not incorporated into, this prospectus, and you should not consider it part of this prospectus or part of any prospectus supplement. Our website address is included in this document as an inactive textual reference only.

The Securities We May Offer

We may offer shares of our common stock and preferred stock, various series of debt securities and/or warrants to purchase any of such securities, either individually or in combination, up to an aggregate dollar amount of $100,000,000, from time to time under this prospectus, together with the applicable prospectus supplement and any related free writing prospectus, at prices and on terms to be determined by market conditions at the time of any offering. We may also offer common stock, preferred stock and/or debt securities upon the exercise of warrants. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

designation or classification;

aggregate principal amount or aggregate offering price;

maturity date, if applicable;

original issue discount, if any;

rates and times of payment of interest or dividends, if any;

redemption, conversion, exercise, exchange or sinking fund terms, if any;

conversion or exchange prices or rates, if any, and, if applicable, any provisions for changes to or adjustments in the conversion or exchange prices or rates and in the securities or other property receivable upon conversion or exchange;

ranking;

restrictive covenants, if any;

voting or other rights, if any; and

material or special U.S. federal income tax considerations, if any.

The applicable prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents we have incorporated by reference. However, no prospectus supplement or free writing prospectus will offer a security that is not registered and described in this prospectus at the time of the effectiveness of the registration statement of which this prospectus is a part.

We may sell the securities directly to investors or to or through agents, underwriters or dealers. We, and our agents or underwriters, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities to or through agents or underwriters, we will include in the applicable prospectus supplement:

the names of those agents or underwriters;

applicable fees, discounts and commissions to be paid to them;

details regarding over-allotment options, if any; and

the net proceeds to us.

THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

Common Stock. We may issue shares of our common stock from time to time. The holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of stockholders. Subject to preferences that may be applicable to any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably such dividends as may be declared by our board of directors out of legally available funds. Upon our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to our common stock. In this prospectus, we have summarized certain general features of the common stock under “Description of Capital Stock — Common stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to any common stock being offered.

Preferred Stock. We may issue shares of our preferred stock from time to time, in one or more series. Our board of directors will determine the designations, voting powers, preferences and rights of the preferred stock, as well as the qualifications, limitations or restrictions thereof, including dividend rights, conversion rights, preemptive rights, terms of redemption or repurchase, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of any series. Convertible preferred stock will be convertible into our common stock or exchangeable for other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

If we sell any series of preferred stock under this prospectus, we will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. In this prospectus, we have summarized certain general features of the preferred stock under “Description of Capital Stock — Preferred stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the series of preferred stock being offered, as well as the complete certificate of designation that contains the terms of the applicable series of preferred stock.

Debt Securities. We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The senior debt securities will rank equally with any other unsecured and unsubordinated debt. The subordinated debt securities will be subordinate and junior in right of payment, to the extent and in the manner described in the instrument governing the debt, to all of our senior indebtedness. Convertible debt securities will be convertible into or exchangeable for our common stock or other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

Any debt securities issued under this prospectus will be issued under one or more documents called indentures, which are contracts between us and a national banking association or other eligible party, as trustee. In this prospectus, we have summarized certain general features of the debt securities under “Description of Debt Securities”. We urge you, however, to read the applicable prospectus supplement (and any free writing prospectus that we may authorize to be provided to you) related to the series of debt securities being offered, as well as the complete indentures that contain the terms of the debt securities. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

Warrants. We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or in combination with common stock, preferred stock and/or debt securities. In this prospectus, we have summarized certain general features of the warrants under “Description of Warrants.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the particular series of warrants being offered, as well as any warrant agreements and warrant certificates that contain the terms of the warrants. We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants.

Any warrants issued under this prospectus may be evidenced by warrant certificates. Warrants also may be issued under an applicable warrant agreement that we enter into with a warrant agent. We will indicate the name and address of the warrant agent, if applicable, in the prospectus supplement relating to the particular series of warrants being offered.

Use of Proceeds

Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, for working capital and general corporate purposes, including research and development expenses and capital expenditures. See “Use of Proceeds” in this prospectus.

NASDAQ Global Market Listing

Our common stock is listed on the NASDAQ Global Market under the symbol “XOMA.” The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the NASDAQ Global Market or other securities exchange of the securities covered by the applicable prospectus supplement.

RISK FACTORS

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and discussed under the section entitled “Risk Factors” contained in our most recent Annual Report on Form 10-K and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus, the documents incorporated by reference and any free writing prospectus that we may authorize for use in connection with this offering. The risks described in these documents are not the only ones we face, but those that we consider to be material. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our common stock to decline, resulting in a loss of all or part of your investment. Please also read carefully the section below entitled “Special Note Regarding Forward-Looking Statements.”

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

Certain statements contained in this prospectus, in the documents incorporated by reference in this prospectus, and in any related prospectus supplement or free writing prospectus that we may authorize, related to the anticipated size of clinical trials, the anticipated timing of initiation of clinical trials, the expected availability of clinical trial results, the sufficiency of our cash resources, the estimated costs of clinical trials and the amounts of certain revenues and certain costs in comparison to prior years, or that otherwise relate to future periods, are forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These statements are based on assumptions that may not prove accurate. Actual results could differ materially from those anticipated due to certain risks inherent in the biotechnology industry and for companies engaged in the development of new products in a regulated market. Among other things:

·	clinical trials may not reach their anticipated size if trials are not initiated or due to enrollment issues such as unavailability of patients, competing product candidates or unanticipated safety issues;

the timing of initiation of or availability of results of clinical trials may be delayed or may never occur as a result of actions or inaction by regulators or our present or future collaboration partners, complications in the design, implementation or third-party approval of clinical trials, complications in the collection or interpretation of statistical data or unanticipated safety issues;

the period for which our cash resources are sufficient could be shortened if expenditures are made earlier or in larger amounts than anticipated or are unanticipated, if anticipated revenue or cost sharing arrangements do not materialize, or if funds are not otherwise available on acceptable terms; and

our revenues may be lower than anticipated, and our costs (including clinical trial costs) may be higher than expected, due to actions or inactions by regulatory authorities or our present or future collaboration partners, unanticipated safety issues or unavailability of additional financing, licensing or collaboration opportunities.

Other risks include those related to:

·	current economic and financial market conditions;

·	the results of discovery research and preclinical testing;

·	the timing or results of pending and future clinical trials (including the design and progress of clinical trials;

·	safety and efficacy of the products being tested;

·	action, inaction or delay by the Food and Drug Administration, European or other regulators or their advisory bodies;

·	analysis or interpretation by, or submission to, these entities or others of scientific data);

·	changes in the status of existing collaborative or licensing relationships;

·	the ability of collaborators, licensees and other third parties to meet their obligations and their discretion in decision-making; our ability to meet the demands of the United States government agency with which we have entered our government contracts;

·	competition;

·	market demand for products;

·	scale-up, manufacturing and marketing capabilities;

·	availability of additional licensing or collaboration opportunities;

·	international operations;

·	share price volatility;

·	our financing needs and opportunities;

·	uncertainties regarding the status of biotechnology patents; and

·	uncertainties as to the costs of protecting intellectual property.

In addition, you should refer to the “Risk Factors” section in the applicable prospectus supplement, or in any free writing prospectuses we may authorize for use in connection with a specific offering, for a discussion of other important factors, risks and uncertainties that may cause our actual results to differ materially from those expressed or implied by these forward-looking statements. Given these other important factors, risks and uncertainties, you should not place undue reliance on these forward-looking statements. Also, these forward-looking statements represent our estimates and assumptions only as of the date such forward-looking statements are made. You should carefully read this prospectus, together with the information incorporated herein by reference as described under the section entitled “Incorporation of Certain Information by Reference,” completely and with the understanding that our actual future results may be materially different from what we expect. We can give no assurances that any of the events anticipated by the forward-looking statements will occur or, if any of them do, what impact they will have on our business, results of operations and financial condition.

You should rely only on information contained or incorporated by reference in this prospectus, the registration statement of which this prospectus is a part, including the exhibits that we have filed with the registration statement, and the applicable prospectus supplement or in any free writing prospectuses we may authorize for use in connection with a specific offering. You should understand that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.

Except as required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. You should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. Before deciding to purchase our securities, you should carefully consider the risk factors discussed and incorporated by reference in this prospectus and any prospectus supplement and, if required, any post-effective amendment to the registration statement of which this prospectus is a part.

USE OF PROCEEDS

The amounts and timing of our use of the net proceeds from this offering will depend on a number of factors, such as the timing and progress of our research and development efforts, the timing and progress of any partnering and commercialization efforts, technological advances and the competitive environment for our products. As of the date of this prospectus, we cannot specify with certainty all of the particular uses for the net proceeds to us from the sale of the securities offered by us hereunder. Accordingly, our management will have broad discretion in the timing and application of these proceeds. Pending application of the net proceeds as described above, we intend to temporarily invest the proceeds in short-term, interest-bearing instruments.

RATIO OF EARNINGS TO FIXED CHARGES

The following table sets forth our ratio of earnings to fixed charges and the amount of deficiency for periods in which the ratio indicates less than one-to-one coverage:

	Six Months Ended June 30, 2012			Year Ended December 31,
				2011			2010			2009		2008			2007
Ratio of earnings to fixed charges (1)		N/A	(2)		N/A	(2)		N/A	(2)		1.9		N/A	(2)		N/A	(2)

(1)	For these purposes, earnings are defined as income before income taxes and fixed charges, and fixed charges include interest expense and the portion of rental expense which is deemed to represent interest.

(2)	Earnings were insufficient to cover fixed charges by $46.6 million for the six months ended June 30, 2012 and $32.7 million, $68.7 million, $45.6 million, and $12.3 million for the years ended December 31, 2011, 2010, 2008 and 2007, respectively.

DESCRIPTION OF CAPITAL STOCK

Our authorized capital stock consists of 138,666,666 shares of common stock, par value $.0075 per share, and 1,000,000 shares of preferred stock, par value $.05 per share. A description of material terms and provisions of our certificate of incorporation and by-laws affecting the rights of holders of our capital stock is set forth below. The description is intended as a summary, and is qualified in its entirety by reference to our certificate of incorporation and the by-laws.

Common stock

Dividends and distributions. The holders of our common stock have the right to receive dividends and distributions, whether payable in cash or otherwise, as may be declared from time to time by our board of directors, from legally available funds. We have not paid cash dividends on the common stock. We currently do not intend to pay dividends and intend to retain any of our earnings for use in our business and the financing of our capital requirements for the foreseeable future. The payment of any future cash dividends on the common stock is necessarily dependent upon our earnings and financial needs, along with applicable legal and contractual restrictions.

Voting rights. Each holder of our common stock is generally entitled to one vote for each share of common stock owned of record on all matters submitted to a vote of our stockholders. Except as otherwise required by law, holders of common stock (as well as holders of any preferred stock entitled to vote with the common stockholders) will generally vote together as a single class on all matters presented to the stockholders for their vote or approval, including the election of directors. Any matter brought before the stockholders for a vote, other than the election of directors, will generally be decided by a majority of the votes cast on the matter, unless the matter is one in which an express provision of the Delaware General Corporation Law, or the DGCL, the certificate of incorporation, the by-laws, the rules or regulations of any stock exchange applicable to us, applicable law or pursuant to any regulation applicable to us or our securities requires a different vote, in which case the express provision will govern and control the decision of the matter. Directors will be elected by a plurality of the votes cast and entitled to vote generally on the election of directors. There are no cumulative voting rights with respect to the election of directors or any other matters.

No preemptive or similar rights. Holders of our common stock have no redemption rights, conversion rights or preemptive rights to purchase or subscribe for our securities.

Right to receive liquidation distributions. In the event of our liquidation, dissolution or winding-up, holders of our common stock will be entitled to share equally in the assets available for distribution after payment of all creditors and the liquidation preferences of our preferred stock (if any).

Restrictions on transfer. Neither our certificate of incorporation nor our by-laws contain any restrictions on the transfer of our common stock. However, in the case of any transfer of shares, there may be restrictions imposed by applicable securities laws or by the terms of restricted share award grants.

Other Provisions. There are no redemption provisions or sinking fund provisions applicable to our common stock.

Transfer Agent and Registrar. The transfer agent and branch registrar for our common stock is Wells Fargo Shareowner Services.

Listing on The NASDAQ Global Market. Our common stock is listed on The NASDAQ Global Market under the symbol “XOMA.”

The rights of the holders of our common stock are subject to, and may be adversely affected by, the rights of holders of shares of any preferred stock that we may designate and issue in the future.

Preferred stock

General. Under our certificate of incorporation, our board of directors is authorized by resolution to divide the preferred stock into series and, with respect to each series, to determine the designations and the powers, preferences and rights, and the qualifications, limitations and restrictions thereof, including the dividend rights, conversion or exchange rights, voting rights, redemption rights and terms, liquidation preferences, sinking fund provisions and the number of shares constituting the series. Our board of directors can, without stockholder approval but subject to the terms of the certificate of incorporation and to any resolution of the stockholders approved by at least 75% of all issued shares entitled to vote in respect thereof, issue preferred stock with voting and other rights that could adversely affect the voting power of the holders of our common stock and which could have certain anti-takeover effects. Before we may issue any series of preferred stock, our board of directors will be required to adopt resolutions creating and designating such series of preferred stock.

The following summary of terms of our preferred stock is not complete. You should refer to the provisions of our certificate of incorporation and by-laws and the resolutions containing the terms of each class or series of the preferred stock which have been or will be filed with the SEC at or prior to the time of issuance of such class or series of preferred stock and described in the applicable prospectus supplement. The applicable prospectus supplement may also state that any of the terms set forth herein are inapplicable to such series of preferred stock, provided that the information set forth in such prospectus supplement does not constitute material changes to the information herein such that it alters the nature of the offering or the securities offered.

Issuances of preferred stock are subject to the applicable rules of The NASDAQ Stock Market or other organizations on whose systems our preferred stock may then be quoted or listed.

Terms. The terms of each series of preferred stock will be described in any prospectus supplement related to such series of preferred stock. The board of directors in approving the creation of a series of preferred stock has authority to determine, and the applicable prospectus supplement may set forth with respect to such series, the following terms, among others:

the designation of the series, which may be by distinguishing number, letter or title;

the number of shares of the series, which number the board of directors may thereafter (except where otherwise provided in a certificate of designation) increase or decrease (but not below the number of shares thereof then outstanding);

the amounts payable on, and the preferences, if any, of shares of the series in respect of dividends, and whether such dividends, if any, shall be cumulative or noncumulative;

dates at which dividends, if any, shall be payable;

the redemption rights and price or prices, if any, for shares of the series;

the terms and amount of any sinking fund provided for the purchase or redemption of shares of the series;

the amounts payable on, and the preferences, if any, of shares of the series in the event of any voluntary or involuntary liquidation, dissolution or winding up of the affairs of the Company;

whether the shares of the series shall be convertible into or exchangeable for shares of any other class or series, or any other security, of ours or any other corporation, and, if so, the specification of such other class or series or such other security, the conversion or exchange price or prices or rate or rates, any adjustments thereof, the date or dates at which such shares shall be convertible or exchangeable and all other terms and conditions upon which such conversion or exchange may be made;

restrictions on the issuance of shares of the same series or of any other class or series; and

the voting rights, if any, of the holders of shares of the series.

The Series A Preferred Stock. We have designated 210,000 shares of our preferred stock as Series A Preferred Stock. There are no shares of Series A Preferred Stock issued and outstanding. Pursuant to the rights of the Series A Preferred Stock, subject to the rights of holders of any shares of any series of preferred stock ranking prior and superior, the holders of Series A Preferred Stock are entitled to receive, when, as and if declared by our board of directors out of funds legally available for the purpose, quarterly dividends payable in cash on the first day of March, June, September and December in each year, commencing on the first dividend payment date after the first issuance of a share or fraction of a share of Series A Preferred Stock, in an amount per share equal to the greater of (a) U.S.$1.00 or (b) 66 2/3 times the aggregate per share amount of all cash dividends, plus 66 2/3 times the aggregate per share amount of all non-cash dividends or other distributions, other than a dividend payable in common stock, declared on the common stock since the immediately preceding dividend payment date, or, with respect to the first dividend payment date, since the first issuance of Series A Preferred Stock.

In addition to any other voting rights required by law, holders of Series A Preferred Stock have the right to vote on all matters submitted to a vote of our stockholders with each share of Series A Preferred Stock entitled to 66 2/3 votes. Except as otherwise provided by law, holders of Series A Preferred Stock and holders of common stock generally vote together as one class on all matters submitted to a vote of our stockholders.

Unless otherwise provided in the rights attaching to a subsequently designated series of our preferred stock, the shares of Series A Preferred Stock rank junior to any other series of preferred stock subsequently issued as to the payment of dividends and distribution of assets on liquidation, dissolution or winding-up and rank senior to the common stock. Upon any liquidation, dissolution or winding-up of us, no distributions shall be made to holders of shares ranking junior to the Series A Preferred Stock unless, prior thereto, the holders of Series A Preferred Stock shall have received an amount equal to accrued and unpaid dividends and distributions, whether or not declared, to the date of such payment, plus an amount equal to the greater of (1) U.S. $100.00 per share or (2) an aggregate amount per share equal to 66 2/3 times the aggregate amount to be distributed per share to holders of common stock or to the holders of shares ranking on parity with the Series A Preferred Stock, except distributions made ratably on the Series A Preferred Stock and all other such parity shares in proportion to the total amount to which the holders of all such shares are entitled upon such liquidation, dissolution or winding-up.

If we enter into any consolidation, amalgamation, merger, combination or other transaction in which shares of common stock are exchanged for or changed into cash, other securities and/or any other property, then any shares of Series A Preferred Stock issued and outstanding shall at the same time be similarly exchanged or changed in an amount per share equal to 66 2/3 times the aggregate amount of cash, securities and/or other property, as the case may be, into which or for which each share of common stock is changed or exchanged.

The Series A Preferred Stock is not redeemable.

Preferred Stock Purchase Rights. Our board of directors has adopted a shareholder rights agreement, or rights agreement. Pursuant to the rights agreement (after giving effect to our reverse stock split), we issued 15 preferred stock purchase rights, or rights, for each issued and outstanding share of common stock. Each right entitles the holder to purchase from us a unit consisting of one one-thousandth of a share of Series A Preferred Stock at a cash exercise price of $30.00 per unit, subject to adjustment.

The rights are attached to all issued and outstanding shares of common stock. The rights will separate from the common stock and will be distributed to holders of common stock upon the earliest of (i) ten business days after the first public announcement that a person or group of affiliated or associated persons (a person or group of affiliated or associated persons being referred to as an Acquiring Person) has acquired beneficial ownership of 20% or more of the common stock then issued and outstanding (the date of said announcement being referred to as the Share Acquisition Date), (ii) ten business days following the commencement of a tender offer or exchange offer that would result in a person or group of persons becoming an Acquiring Person or (iii) the declaration by our board of directors that any person is an “Adverse Person” (the earliest of such dates being referred to as the Distribution Date). For purposes of the rights agreement, beneficial ownership of our common stock is generally determined pursuant the applicable rules and regulations under the Exchange Act and beneficial owners of new notes or existing notes will be considered beneficial owners of the shares of common stock into which their notes are convertible.

Our board of directors may generally declare a person to be an Adverse Person after a declaration that such person has become the beneficial owner of 10% or more of the issued and outstanding shares of common stock and a determination that (i) such beneficial ownership by such person is intended to cause or is reasonably likely to cause us to repurchase the common stock owned by such person or to cause us to enter into other transactions not in our best long-term interests or (ii) such beneficial ownership is reasonably likely to cause a material adverse impact on our business or prospects. The rights are not exercisable until the Distribution Date and will expire on December 31, 2012, unless previously redeemed or exchanged by us.

In the event that a person becomes an Acquiring Person or our board of directors determines that a person is an Adverse Person, each holder of a right will thereafter have the right (each right being referred to as a Subscription Right) to receive upon exercise that number of units of Series A Preferred Stock having a market value of two times the exercise price of the rights. In the event that, at any time following the Share Acquisition Date, (i) we consolidate with, or merge or amalgamate with and into, any person, and we are not the surviving corporation; (ii) any person consolidates or amalgamates with us, or merges or amalgamates with and into us and we are the continuing or surviving corporation of such transaction and, in connection with such transaction, all or part of the common stock are changed into or exchanged for other securities of any other person or cash or any other property, or (iii) 50% or more of our assets are sold or otherwise transferred, provision shall be made so that each holder of a right shall thereafter have the right (each right being referred to as a Merger Right) to receive, upon exercise, common stock of the acquiring company having a market value equal to two times the exercise price of the rights. Rights that are beneficially owned by an Acquiring or Adverse Person may, under certain circumstances, become null and void.

At any time after a person becomes an Acquiring Person or our board of directors determines that a person is an Adverse Person, our board of directors may exchange all or any part of the then outstanding and exercisable rights for common stock or units of Series A Preferred Stock at an exchange ratio of one share of common stock or one unit of Series A Preferred Stock per right. Notwithstanding the foregoing, our board of directors generally will not be empowered to effect such exchange at any time after any person becomes the beneficial owner of 50% or more of the common stock then issued and outstanding.

The rights may be redeemed in whole, but not in part, at a price of U.S. $.015 per right by our board of directors at any time prior to the date on which a person is declared to be an Adverse Person, the tenth business day after the Share Acquisition Date, the occurrence of an event giving rise to the Merger Right or the expiration date of the rights agreement.

Prior to the earlier of the Distribution Date and the Share Acquisition Date, our board may amend the rights agreement as we deem necessary or desirable without the approval of any holders of rights or common stock. From and after the earlier of the Distribution Date and the Share Acquisition Date, the rights agreement may be amended without the approval of any holders of rights only to (i) cure an ambiguity, (ii) correct defective or inconsistent provisions, (iii) shorten or lengthen any time period in the rights agreement if directors in office prior to the acquisition of shares continue to represent a majority of the board, or (iv) change provisions as we deem necessary, but that will not adversely affect the interests of holders of the rights. Under no circumstances, however, can the rights agreement be amended to lengthen a time period relating to when the rights may be redeemed if the rights are not then redeemable.

Outstanding Warrants

In March 2012, we issued warrants to purchase 14,834,577 shares of our common stock in connection with an underwritten offering, which are immediately exercisable at an exercise price of $1.76 per share and have a five-year term. As of June 30, 2012, 14,829,167 of these warrants were outstanding.

In December of 2011, we issued warrants in connection with a debt financing, which entitle the holder to purchase up to an aggregate of 263,158 unregistered shares of our common stock at an exercise price equal to $1.14 per share, are immediately exercisable and will expire on December 30, 2016. In February of 2010, we issued warrants to purchase 1,260,000 shares of our common stock in connection with an underwritten offering, which are exercisable beginning six months and one day after issuance and have a five-year term and an exercise price of $10.50 per share. In June of 2009, we issued warrants to certain institutional investors as part of a registered direct offering, which represent the right to acquire an aggregate of up to 347,826 shares of common stock over a five year period beginning December 11, 2009, at an exercise price of $19.50 per share. As of June 30, 2012, all of the warrants issued in December of 2011, February of 2010 and June of 2009 were outstanding.

Anti-takeover effects of provisions of our certificate of incorporation and by-laws and Delaware law

Certificate of incorporation and by-laws. Our certificate of incorporation authorizes our board of directors to issue up to 1,000,000 shares of preferred stock without stockholder approval and to set the rights, preferences and other designations, including voting rights, of those shares as the board of directors may determine. In addition, our by-laws require certain procedures to be followed and time periods to be met for any stockholder to propose matters to be considered at annual meetings of stockholders, including nominating directors for election at those meetings. Our by-laws also provide that our board of directors is able to elect a director to fill a vacancy created by the expansion of the board of directors or due to the resignation or departure of an existing board member.

Section 203 of the Delaware General Corporation Law. We are subject to the provisions of Section 203 of the DGCL regulating corporate takeovers. This section prevents some Delaware corporations from engaging, under some circumstances, in a business combination, which includes a merger or sale of at least 10% of the corporation’s assets with any interested stockholder, meaning a stockholder who, together with affiliates and associates, owns or, within three years prior to the determination of interested stockholder status, did own 15% or more of the corporation’s outstanding voting stock, unless:

the transaction is approved by the board of directors prior to the time that the interested stockholder became an interested stockholder;

upon consummation of the transaction which resulted in the stockholder’s becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced; or

at or subsequent to such time that the stockholder became an interested stockholder the business combination is approved by the board of directors and authorized at an annual or special meeting of stockholders by at least two-thirds of the outstanding voting stock which is not owned by the interested stockholder.

A Delaware corporation may “opt out” of these provisions with an express provision in its original certificate of incorporation or an express provision in its certificate or incorporation or by-laws resulting from a stockholders’ amendment approved by a majority of the outstanding voting shares. We have not “opted out” of these provisions and do not plan to do so. The statute could prohibit or delay mergers or other takeover or change in control attempts and, accordingly, may discourage attempts to acquire us.

The provisions of our rights agreement, described above, as well as our organizational documents and the DGCL, alone or in combination with each other, may discourage transactions involving actual or potential changes of control, including transactions that otherwise could involve payment of a premium over prevailing market prices to holders of common stock, could limit the ability of stockholders to approve transactions that they may deem to be in their best interests, and could make it considerably more difficult for a potential acquirer to replace management.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Wells Fargo Shareowner Services.

Listing on the NASDAQ Global Market

Our common stock is listed on the NASDAQ Global Market under the symbol “XOMA”. The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the NASDAQ Global Market or any securities market or other exchange of the preferred stock covered by such prospectus supplement.

DESCRIPTION OF DEBT SECURITIES

We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue the debt securities under the indenture that we will enter into with trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with “original issue discount,” or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.

We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

the title of the series of debt securities;

any limit upon the aggregate principal amount that may be issued;

the maturity date or dates;

the form of the debt securities of the series;

the applicability of any guarantees;

whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

whether the debt securities rank as senior debt, senior subordinated debt, subordinated debt or any combination thereof, and the terms of any subordination;

if the price (expressed as a percentage of the aggregate principal amount thereof) at which such debt securities will be issued is a price other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof, or if applicable, the portion of the principal amount of such debt securities that is convertible into another security or the method by which any such portion shall be determined;

the interest rate or rates, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

our right, if any, to defer payment of interest and the maximum length of any such deferral period;

if applicable, the date or dates after which, or the period or periods during which, and the price or prices at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

the date or dates, if any, on which, and the price or prices at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

any and all terms, if applicable, relating to any auction or remarketing of the debt securities of that series and any security for our obligations with respect to such debt securities and any other terms which may be advisable in connection with the marketing of debt securities of that series;

whether the debt securities of the series shall be issued in whole or in part in the form of a global security or securities; the terms and conditions, if any, upon which such global security or securities may be exchanged in whole or in part for other individual securities; and the depositary for such global security or securities;

if applicable, the provisions relating to conversion or exchange of any debt securities of the series and the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders’ option) conversion or exchange features, the applicable conversion or exchange period and the manner of settlement for any conversion or exchange;

if other than the full principal amount thereof, the portion of the principal amount of debt securities of the series which shall be payable upon declaration of acceleration of the maturity thereof;

additions to or changes in the covenants applicable to the particular debt securities being issued, including, among others, the consolidation, merger or sale covenant;

additions to or changes in the events of default with respect to the securities and any change in the right of the trustee or the holders to declare the principal, premium, if any, and interest, if any, with respect to such securities to be due and payable;

additions to or changes in or deletions of the provisions relating to covenant defeasance and legal defeasance;

additions to or changes in the provisions relating to satisfaction and discharge of the indenture;

additions to or changes in the provisions relating to the modification of the indenture both with and without the consent of holders of debt securities issued under the indenture;

the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars;

whether interest will be payable in cash or additional debt securities at our or the holders’ option and the terms and conditions upon which the election may be made;

the terms and conditions, if any, upon which we will pay amounts in addition to the stated interest, premium, if any and principal amounts of the debt securities of the series to any holder that is not a “United States person” for federal tax purposes;

any restrictions on transfer, sale or assignment of the debt securities of the series; and

any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, any other additions or changes in the provisions of the indenture, and any terms that may be required by us or advisable under applicable laws or regulations.

Conversion or Exchange Rights

We will set forth in the prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities or other property or assets. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities or units of other property or assets that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquirer of such assets must assume all of our obligations under the indenture or the debt securities, as appropriate..

Events of Default Under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:

if we fail to pay any installment of interest on any series of debt securities, as and when the same shall become due and payable, and such default continues for a period of 90 days; provided, however, that a valid extension of an interest payment period by us in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of interest for this purpose;

if we fail to pay the principal of, or premium, if any, on any series of debt securities as and when the same shall become due and payable whether at maturity, upon redemption, by declaration or otherwise, or in any payment required by any sinking or analogous fund established with respect to such series; provided, however, that a valid extension of the maturity of such debt securities in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of principal or premium, if any;

if we fail to observe or perform any other covenant or agreement contained in the debt securities or the indenture, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive written notice of such failure, requiring the same to be remedied and stating that such is a notice of default thereunder, from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

if specified events of bankruptcy, insolvency or reorganization occur.

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

the direction so given by the holder is not in conflict with any law or the applicable indenture; and

subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

A holder of the debt securities of any series will have the right to institute a proceeding under the indenture or to appoint a receiver or trustee, or to seek other remedies only if:

the holder has given written notice to the trustee of a continuing event of default with respect to that series;

the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, and such holders have offered reasonable indemnity to the trustee to institute the proceeding as trustee; and

the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indenture.

Modification of Indenture; Waiver

We and the trustee may change an indenture without the consent of any holders with respect to specific matters:

to cure any ambiguity, defect or inconsistency in the indenture or in the debt securities of any series;

to comply with the provisions described above under “Description of Debt Securities—Consolidation, Merger or Sale;”

to provide for uncertificated debt securities in addition to or in place of certificated debt securities;

to add to our covenants, restrictions, conditions or provisions such new covenants, restrictions, conditions or provisions for the benefit of the holders of all or any series of debt securities, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred upon us in the indenture;

to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

to make any change that does not adversely affect the interests of any holder of debt securities of any series in any material respect;

to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided above under “Description of Debt Securities—General” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

to evidence and provide for the acceptance of appointment under any indenture by a successor trustee; or

to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act.

In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

extending the fixed maturity of any debt securities of any series;

reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any series of any debt securities; or

reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

provide for payment;

replace stolen, lost or mutilated debt securities of the series;

pay principal of and premium and interest on any debt securities of the series;

maintain paying agencies;

hold monies for payment in trust;

recover excess money held by the trustee;

compensate and indemnify the trustee; and

appoint any successor trustee.

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company, or DTC, or another depositary named by us and identified in a prospectus supplement with respect to that series. To the extent the debt securities of a series are issued in global form and as book-entry, a description of terms relating will be set forth in the applicable prospectus supplement.

At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indenture and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act of 1939 is applicable.

DESCRIPTION OF WARRANTS

The following description, together with the additional information that we include in any applicable prospectus supplement and in any related free writing prospectus that we may authorize to be distributed to you, summarizes the material terms and provisions of the warrants that we may offer under this prospectus, which may be issued in one or more series. Warrants may be offered independently or in combination with other securities offered by any prospectus supplement. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The following description of warrants will apply to the warrants offered by this prospectus unless we provide otherwise in the applicable prospectus supplement. The applicable prospectus supplement for a particular series of warrants may specify different or additional terms.

We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants. The following summaries of material terms and provisions of the warrants are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements applicable to a particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplement related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectuses, and the complete form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements, that contain the terms of the warrants.

General

We will describe in the applicable prospectus supplement the terms of the series of warrants being offered, including:

the offering price and aggregate number of warrants offered;

the currency for which the warrants may be purchased;

if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;

in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;

the terms of any rights to redeem or call the warrants;

any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

the dates on which the right to exercise the warrants will commence and expire;

the manner in which the warrant agreements and warrants may be modified;

a discussion of any material or special U.S. federal income tax considerations of holding or exercising the warrants;

the terms of the securities issuable upon exercise of the warrants; and

any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including:

in the case of warrants to purchase debt securities, the right to receive payments of principal of, or premium, if any, or interest on, the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture; or

in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or, payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. The warrants may be exercised as set forth in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the close of business on the expiration date set forth in the prospectus supplement relating to the warrants offered thereby. After the close of business on the expiration date, unexercised warrants will become void.

Upon receipt of payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable upon such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining warrants.

Governing Law

Unless we otherwise specify in the applicable prospectus supplement, the warrants and any warrant agreements will be governed by and construed in accordance with the laws of the State of New York.

Enforceability of Rights by Holders of Warrants

Each warrant agent, if any, will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

LEGAL OWNERSHIP OF SECURITIES

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of the indenture or for other purposes. In such an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.

Special Considerations For Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

the performance of third party service providers;

how it handles securities payments and notices;

whether it imposes fees or charges;

how it would handle a request for the holders’ consent, if ever required;

whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, DTC will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under the section entitled “Special Situations When a Global Security Will Be Terminated” in this prospectus. As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations For Global Securities

The rights of an indirect holder relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only in the form of a global security, an investor should be aware of the following:

an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;

an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;

an investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security;

we and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security, nor do we or any applicable trustee supervise the depositary in any way;

the depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

Unless we provide otherwise in the applicable prospectus supplement, the global security will terminate when the following special situations occur:

if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

if we notify any applicable trustee that we wish to terminate that global security; or

if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the applicable prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

PLAN OF DISTRIBUTION

We may sell the securities from time to time pursuant to underwritten public offerings, direct sales to the public, negotiated transactions, block trades or a combination of these methods. We may sell the securities to or through underwriters or dealers, through agents, or directly to one or more purchasers. We may distribute securities from time to time in one or more transactions:

at a fixed price or prices, which may be changed;

at market prices prevailing at the time of sale;

at prices related to such prevailing market prices; or

at negotiated prices.

A prospectus supplement or supplements (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the securities, including, to the extent applicable:

the name or names of the underwriters, if any;

the purchase price of the securities or other consideration therefor, and the proceeds, if any, we will receive from the sale;

any over-allotment options under which underwriters may purchase additional securities from us;

any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

any public offering price;

any discounts or concessions allowed or reallowed or paid to dealers; and

any securities exchange or market on which the securities may be listed.

Only underwriters named in the prospectus supplement will be underwriters of the securities offered by the prospectus supplement.

If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement, other than securities covered by any over-allotment option. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time. We may use underwriters with whom we have a material relationship. We will describe in the prospectus supplement, naming the underwriter, the nature of any such relationship.

We may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities and we will describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

We may authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

We may provide agents and underwriters with indemnification against civil liabilities, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us in the ordinary course of business.

All securities we may offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

Any underwriter may engage in over-allotment, stabilizing transactions, short-covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Over-allotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum price. Syndicate-covering or other short-covering transactions involve purchases of the securities, either through exercise of the over-allotment option or in the open market after the distribution is completed, to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.

Any underwriters or agents that are qualified market makers on the NASDAQ Global Market may engage in passive market making transactions in the common stock on the NASDAQ Global Market in accordance with Regulation M under the Exchange Act, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and any applicable prospectus supplement.

LEGAL MATTERS

Unless otherwise indicated in the applicable prospectus supplement, the validity of the securities offered by this prospectus, and any supplement thereto, will be passed upon for us by Cooley LLP, Palo Alto, California.

EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2011, as set forth in their report, which is incorporated by reference in this prospectus and elsewhere in the registration statement of which this prospectus forms a part. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth in the registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov. You may also read and copy any document we file at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 000-14710):

our annual report on Form 10-K for the year ended December 31, 2011, filed on March 14, 2012 (file no. 000-14710);

the information specifically incorporated by reference into the 2011 Form 10-K from our definitive proxy statement on Schedule 14A, which was filed on April 11, 2012;

our quarterly reports on Form 10-Q for the quarterly periods ended March 31, 2012, and June 30, 2012, filed on May 8, 2012, and August 7, 2012, respectively (file no. 000-14710);

our Current Reports on Form 8-K filed on January 3, 2012, January 6, 2012 (two reports), January 17, 2012, February 14, 2012, March 7, 2012, May 31, 2012, July 13, 2012, and July 23, 2012; and

We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including those made after the date of the initial filing of the registration statement of which this prospectus is a part and prior to effectiveness of such registration statement, until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus and will become a part of this prospectus from the date that such documents are filed with the SEC. Information in such future filings updates and supplements the information provided in this prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

You can request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:

XOMA Corporation

2910 Seventh Street

Berkeley, California 94710

(510) 204-7200

Attn: Chief Financial Office