SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                   ----------

                                    Form 11-K

                                   ----------


          [X] ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES
                              EXCHANGE ACT OF 1934

                   For the fiscal year ended December 31, 2003
                                             -----------------


                         Commission file number 2-84723
                                                -------


                              --------------------


       THE SCHERING-PLOUGH PUERTO RICO EMPLOYEES' RETIREMENT SAVINGS PLAN
                              (Full Title of Plan)


                           Schering-Plough Corporation
                            2000 Galloping Hill Road
                              Kenilworth, NJ 07033
     (Name of Issuer of Securities Held Pursuant to the Plan and Address of
                          Principal Executive Offices)

THE SCHERING-PLOUGH PUERTO RICO
EMPLOYEES' RETIREMENT SAVINGS PLAN

TABLE OF CONTENTS



                                                                            Page
                                                                            ----
                                                                         
REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM                        3

FINANCIAL STATEMENTS:
     Statements of Net Assets Available for Benefits
        as of December 31, 2003 and 2002                                       4

     Statement of Changes in Net Assets Available for Benefits
        for the Year Ended December 31, 2003                                   5

     Notes to Financial Statements                                          6-10

SUPPLEMENTAL SCHEDULE:
     Form 5500, Schedule H, Part IV, Line 4i - Schedule of Assets
     (Held at End of Year) as of December 31, 2003                            11

SIGNATURES                                                                    12

EXHIBIT I - Consent of Independent Registered Public Accounting Firm          13




----------
All other schedules required by Section 2520.103-10 of the Department of Labor's
Rules and Regulations for Reporting and Disclosure under the Employee Retirement
Income Security Act of 1974 have been omitted because they are not applicable.


                                        2

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Participants of
The Schering-Plough Puerto Rico Employees' Retirement Savings Plan:

We have audited the accompanying statements of net assets available for benefits
of The Schering-Plough Puerto Rico Employees' Retirement Savings Plan (the
"Plan") as of December 31, 2003 and 2002, and the related statement of changes
in net assets available for benefits for the year ended December 31, 2003. These
financial statements are the responsibility of the Plan's management. Our
responsibility is to express an opinion on these financial statements based on
our audits.

We conducted our audits in accordance with the standards of the Public Company
Accounting Oversight Board (United States). Those standards require that we plan
and perform the audit to obtain reasonable assurance about whether the financial
statements are free of material misstatement. An audit also includes examining,
on a test basis, evidence supporting the amounts and disclosures in the
financial statements, assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation. We believe that our audits provide a reasonable basis
for our opinion.

In our opinion, such financial statements present fairly, in all material
respects, the net assets available for benefits of the Plan as of December 31,
2003 and 2002, and the changes in net assets available for benefits for the year
ended December 31, 2003 in conformity with accounting principles generally
accepted in the United States of America.

Our audits were conducted for the purpose of forming an opinion on the basic
financial statements taken as a whole. The supplemental Schedule of Assets Held
at End of Year is presented for the purpose of additional analysis and is not a
required part of the basic financial statements, but is supplementary
information required by the Department of Labor's Rules and Regulations for
Reporting and Disclosure under the Employee Retirement Income Security Act of
1974. This schedule is the responsibility of the Plan's management. Such
schedule has been subjected to the auditing procedures applied in our audit of
the basic 2003 financial statements, and, in our opinion, is fairly stated in
all material respects when considered in relation to the basic financial
statements taken as a whole.


/s/ Deloitte & Touche LLP
Parsippany, New Jersey
June 25, 2004


                                        3

THE SCHERING-PLOUGH PUERTO RICO
EMPLOYEES' RETIREMENT SAVINGS PLAN

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS
DECEMBER 31, 2003 AND 2002



                                                           2003         2002
                                                           ----         ----
                                                               
INVESTMENTS:
   Vanguard funds                                       $20,279,825  $15,470,824

   Schering-Plough stock fund                             2,913,363    3,125,535

   Loan fund                                              1,826,086    1,912,905
                                                        -----------  -----------
TOTAL INVESTMENTS                                        25,019,274   20,509,264

Participant contributions receivable                        185,594      119,727
                                                        -----------  -----------

NET ASSETS AVAILABLE FOR BENEFITS                       $25,204,868  $20,628,991
                                                        ===========  ===========






See Notes to Financial Statements.


                                       4

THE SCHERING-PLOUGH PUERTO RICO
EMPLOYEES' RETIREMENT SAVINGS PLAN

STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS
YEAR ENDED DECEMBER 31, 2003


                                                                
Additions to net assets attributed to:

     Investment income:
       Dividend income, registered investment companies            $   303,944
       Dividend income, Schering-Plough Stock Fund                      88,947
       Interest income, participant loans                              105,825
       Net appreciation in fair value of investments                 2,645,291
                                                                   -----------
     Total investment income                                         3,144,007

     Participant contributions                                       3,058,446
                                                                   -----------


         Total additions                                             6,202,453
                                                                   -----------

Deductions from net assets attributed to:

     Benefits paid to participants                                   1,626,576
                                                                   -----------


Increase in net assets                                               4,575,877

Net assets available for benefits:
  Beginning of year                                                 20,628,991
                                                                   -----------

  End of year                                                      $25,204,868
                                                                   ===========




See Notes to Financial Statements.


                                       5

THE SCHERING-PLOUGH PUERTO RICO
EMPLOYEES' RETIREMENT SAVINGS PLAN

NOTES TO FINANCIAL STATEMENTS

1.    DESCRIPTION OF PLAN

      The Schering-Plough Puerto Rico Employees' Retirement Savings Plan (the
      "Plan") is a defined contribution plan established effective April 1,
      1990. The Plan is intended to encourage retirement savings by eligible
      employees of Schering-Plough Products LLC (the "Sponsor" or the "Company")
      and any of its affiliated companies that adopt the Plan. Vanguard
      Fiduciary Trust Company ("Vanguard"), the recordkeeper, is a trust company
      incorporated under Chapter 10 of the Pennsylvania Banking Code, and a
      wholly-owned subsidiary of The Vanguard Group, Inc. Banco Santander serves
      as the Plan's trustee.

      Generally, all Puerto Rico employees of Schering-Plough Products LLC and
      Schering-Plough del Caribe, Inc. are eligible to participate in the Plan
      on the date of employment. The participants may elect to have their salary
      deferral contributions allocated to any of the investment funds available
      under this Plan.

      The following brief description of the Plan is provided for general
      information purposes only. Participants should refer to the Plan document
      for more complete information.

      SALARY DEFERRAL CONTRIBUTIONS - The Plan is designed to permit eligible
      employees to elect to have a portion of their salary contributed to the
      Plan on their behalf ("Salary Deferral Contributions"). Under the
      provisions of the Plan, Salary Deferral Contributions can range from 1% to
      10% of the employee's earnings, in increments of 1%, subject to certain
      regulated limits. Salary Deferral Contributions and any earnings accrued
      thereon are fully and immediately vested to the participant.

      PARTICIPANT ACCOUNTS AND VESTING - Each participant's account is credited
      with the participant's contribution and allocations of Plan earnings
      (losses). Allocations are based on participant earnings or account
      balances, as defined. Participants have a non-forfeitable right to their
      contributions plus (minus) actual earnings (losses) thereon which vest
      fully and immediately.

      INVESTMENT OPTIONS - Upon enrollment in the Plan, participants may direct
      their contributions into any of the following Vanguard investment options:

      -     Vanguard 500 Index Fund Investor Shares

      -     Vanguard Explorer Fund Investor Shares

      -     Vanguard Intermediate-Term Corporate Fund Investor Shares

      -     Vanguard International Growth Fund Investor Shares

      -     Vanguard LifeStrategy Conservative Growth Fund

      -     Vanguard LifeStrategy Growth Fund

      -     Vanguard LifeStrategy Income Fund

      -     Vanguard LifeStrategy Moderate Growth Fund

      -     Vanguard Short-Term Corporate Fund Investor Shares

      -     Vanguard Treasury Money Market Fund

      -     Vanguard U.S. Growth Fund Investor Shares

      -     Vanguard Wellington Fund Investor Shares

      -     Vanguard Windsor Fund Investor Shares


                                       6

      Participants may also direct their contributions to the:

      -     Schering-Plough Stock Fund - This fund is comprised of
            Schering-Plough common stock and a small percentage of cash as
            required for liquidity purposes. Participants may contribute up to a
            maximum investment election of 50% of their Salary Deferral
            Contribution into this fund or allocate no more than 50% of the
            value of his or her accounts at the time of reallocation to this
            fund.

      Loan Fund - Participants may borrow from their fund accounts up to the
      lesser of one half of their account or $50,000 (reduced by any outstanding
      loans). Loan transactions are treated as a transfer between the investment
      funds and the Loan Fund. These loans, which are secured by the
      participants' individual fund accounts, bear a fixed rate of interest as
      determined to be reasonable by The Schering-Plough Puerto Rico Employees'
      Retirement Savings Plan Committee, and are repayable over periods not
      exceeding five years, except loans relating to a principal residence which
      are repayable over a period not to exceed 20 years.

      PAYMENT OF BENEFITS - On termination of service due to death, disability
      or retirement, a participant may elect to receive either a lump sum amount
      or installments not to exceed the life expectancy of the participant and
      the participant's beneficiary. For termination of service due to other
      reasons, a participant may receive the value of the account as a lump sum
      distribution. Alternatively, all participants can elect to defer receipt
      of their account up to age 70 -1/2. Distribution of all or a portion of a
      participant's account, prior to termination of employment, may be granted
      by the Sponsor in the case of financial hardship. Active participants may
      elect to withdraw all or a portion of their accounts at any time after age
      59 1/2.

      CHANGES TO PLAN ON JANUARY 1, 2004 - Effective January 1, 2004, the
      Sponsor amended the Plan to incorporate a company matching contribution.
      All employees eligible to participate in the Plan will receive a company
      provided matching contribution (dollar for dollar) on the first 5% of
      employee Salary Deferral Contributions. The company matching contribution
      and any earnings accrued thereon are fully and immediately vested.

2.    SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

      BASIS OF ACCOUNTING - The financial statements of the Plan have been
      prepared on an accrual basis in accordance with accounting principles
      generally accepted in the United States of America.

      The financial statements were prepared in accordance with the financial
      reporting requirements of the Employee Retirement Income Security Act of
      1974 ("ERISA") as permitted by the Securities and Exchange Commission.

      INVESTMENT VALUATION AND INCOME RECOGNITION - The Plan's investments are
      stated at fair value. Shares of registered investment companies are valued
      at quoted market prices which represent the net asset value of shares held
      by the Plan at year-end.

      The Schering-Plough Stock Fund is valued using the unit accounting method
      whereby a participant's account value is expressed in units of
      participation rather than number of shares of Schering-Plough common
      stock.

      The closing stock prices of Schering-Plough Corporation common stock at
      December 31, 2003 and December 31, 2002 were $17.39 and $22.20,
      respectively.

                                       7

      Purchases and sales of securities are recorded on a trade-date basis.
      Interest income is recorded on the accrual basis. Dividend income is
      recorded on the ex-dividend date. Dividends received in the
      Schering-Plough Stock Fund are reinvested in Schering-Plough common stock
      units.

      Participant loans are valued at cost which approximates fair value.

      WITHDRAWALS AND BENEFIT PAYMENTS - Withdrawals and benefit payments are
      recorded when paid.

      USE OF ESTIMATES - The preparation of financial statements in conformity
      with generally accepted accounting principles requires management to make
      estimates and assumptions that affect the reported amounts of assets and
      liabilities and changes therein, and disclosure of contingent assets and
      liabilities. Actual results could differ from those estimates.

      RISKS AND UNCERTAINTIES - The Plan provides for various investment
      options. Investment securities, in general, are exposed to various risks,
      such as interest rate, credit and overall market volatility. Due to the
      level of risk associated with certain investment securities, it is
      reasonably possible that changes in value of investment securities will
      occur in the near term and that such changes could materially affect
      participants' account balances and the amounts reported in the statements
      of net assets available for benefits.

3.    PLAN TERMINATION

      Although it has not expressed any intent to do so, the Sponsor has the
      right under the Plan to terminate the Plan subject to provisions of ERISA.

4.    TAX STATUS

      The Plan was amended and restated effective January 1, 1995. The plan
      received a favorable determination letter dated February 18, 1997 issued
      by the Puerto Rico Department of the Treasury stating that the Plan meets
      the requirements of Section 1165(a) of the Puerto Rico Internal Revenue
      Code of 1995, as amended (the "PR Code"). The Plan was also amended
      effective January 1, 1996 and October 1, 1996 pursuant to Amendment No. 2.
      The Puerto Rico Department of the Treasury issued a favorable
      determination letter dated April 14, 1997 in connection with the
      qualification of Amendment No. 2.

      The trust of the Plan is intended to be exempt from taxation under Section
      1165(a) of the PR Code, and pursuant to Section 1022(i)(1) of the Employee
      Retirement Income Security Act of 1974, as amended, under Section 501(a)
      of the United States Internal Revenue Code of 1986, as amended.

      As long as the Plan is qualified under the PR Code and related
      regulations, participants will generally not be taxed on salary-deferred
      contributions until the year received. In addition, the earnings
      attributable to such contributions held by the trustee are also generally
      exempt from taxation until the taxable year in which they are withdrawn by
      or distributed to the participant.

      The Plan's tax counsel believes that the Plan is designed in compliance
      with the applicable requirements of the Puerto Rico Internal Revenue Code,
      and the Plan Administrator believes that the Plan is being operated in
      compliance with the applicable requirements of the Puerto Rico Internal
      Revenue Code.

5.    RELATED-PARTY TRANSACTIONS


                                       8

      Contributions are transmitted from the trustee, Banco Santander, to the
      recordkeeper, Vanguard, which invests cash received, interest and dividend
      income and makes distributions to the participants. The recordkeeper also
      administers the collection of interest and principal on the participant
      loans. These transactions qualify as permitted party-in-interest
      transactions.

      Certain Plan investments are shares of mutual funds managed by the
      recordkeeper. These transactions qualify as permitted party-in-interest
      transactions.

      Certain Plan investments are shares of the Company's stock. These
      transactions qualify as permitted party-in-interest transactions.

      Certain administrative functions are performed by officers or employees of
      the Sponsor who also may be participants in the Plan. These actions
      qualify as permitted party-in-interest activities. No such officer or
      employee receives compensation from the Plan.

      All plan administration expenses are paid by the Sponsor.

6.    NET APPRECIATION (DEPRECIATION) IN FAIR VALUE OF INVESTMENTS

      During 2003, the Plan's investments (including gains and losses on
      investments bought and sold, as well as held during the year) appreciated
      (depreciated) in value as follows:

      *Vanguard 500 Index Fund Investor Shares                 $ 1,680,484
      *Vanguard Windsor Fund Investor Shares                       906,573
      *Vanguard Explorer Fund Investor Shares                      439,707
      *Vanguard Wellington Fund Investor Shares                    107,590
      *Vanguard International Growth Fund Investor Shares          102,017
      *Vanguard U.S. Growth Fund Investor Shares                    26,158
      *Vanguard LifeStrategy Moderate Growth Fund                   24,923
      *Vanguard LifeStrategy Growth Fund                            21,987
      *Vanguard LifeStrategy Conservative Growth Fund                8,331
      *Vanguard LifeStrategy Income Fund                             6,404
      *Vanguard Short-Term Corporate Fund Investor Shares            1,722
      *Vanguard Intermediate-Term Corporate Fund Investor
      Shares                                                          (600)
      *Schering-Plough Stock Fund                                 (680,005)
                                                               -----------
      Net Appreciation in Fair Value of Investments            $ 2,645,291
                                                               ===========

     *Permitted party-in-interest to the Plan.


                                       9

7.    INVESTMENTS

      The following investments represented 5% or more of the Plan's net assets
      available for benefits at:



                                                            December 31,
                                                         2003           2002
                                                         ----           ----
                                                              
      ***Vanguard 500 Index Fund Investor Shares     $8,128,468     $5,901,432

      ***Vanguard Windsor Fund Investor Shares        3,523,905      2,528,752

      ***Vanguard Treasury Money Market Fund          2,945,416      2,937,481

      ***Schering-Plough Stock Fund                   2,913,363      3,125,535

      ***Loan Fund                                    1,826,086      1,912,905

     ***Vanguard Explorer Fund Investor Shares        1,800,510            * *

     ***Vanguard Short-term
        Corporate Fund Investor Shares                        *      1,155,091


* This fund did not exceed 5% as of December 31, 2003.

** This fund did not exceed 5% as of December 31, 2002.

***Permitted party-in-interest to the Plan.


                                       10

THE SCHERING-PLOUGH PUERTO RICO                                       SCHEDULE H
EMPLOYEES' RETIREMENT SAVINGS PLAN

FORM 5500, SCHEDULE H, PART IV, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF
YEAR)
AS OF DECEMBER 31, 2003
Employer Identification Number: 52-2170309
Plan number: 002



           Identity of
           Issuer,        Description of investment
           Borrower,      including maturity date, rate of
           Lessor or      interest, collateral,
           Similar        par or maturity                           Current
           Party          value                                      Value
           -----          -----                                      -----
                                                        
     *    Vanguard        500 Index Fund Investor Shares         $ 8,128,468

     *    Vanguard        Windsor Fund Investor Shares             3,523,905

     *    Vanguard        Treasury Money Market Fund               2,945,416

     *    Vanguard        Explorer Fund Investor Shares            1,800,510

     *    Vanguard        Short-Term Corporate Fund
                            Investor Shares                        1,116,410

     *    Vanguard        Intermediate -Term Corporate Fund
                            Investor Shares                          854,501

     *    Vanguard        Wellington Fund Investor Shares            850,558

     *    Vanguard        International Growth Fund                  440,804
                          Investor Shares

     *    Vanguard        LifeStrategy Moderate Growth Fund          178,380

     *    Vanguard        LifeStrategy Growth Fund                   133,306

     *    Vanguard        U.S. Growth Fund Investor Shares           126,716

     *    Vanguard        LifeStrategy Income Fund                   101,194

     *    Vanguard        LifeStrategy Conservative Growth            79,657
                                                                  ----------
                          Fund

                          Total Vanguard Registered
                          Investment Company Funds                20,279,825
                                                                  ----------

     *   Schering -       Schering-Plough Stock Fund               2,913,363
           Plough
        Corporation

     *    Various         Outstanding loan balance
        participants      (interest rates ranging from
                          5.25% to 6.50%, maturing from 1
                          to 20 years)                             1,826,086
                                                                  ----------

                          Total Assets Held at End of Year       $25,019,274
                                                                 ===========


*Permitted party-in-interest to the Plan.

Cost information is not required for participant-directed investments and
therefore is not included.


                                       11

                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
trustees (or other persons who administer the Plan) have duly caused this Annual
Report to be signed on its behalf by the undersigned hereunto duly authorized.

                                      The Schering-Plough Puerto Rico Employees'
                                      Retirement Savings Plan

Date:  June 28, 2004                  By: /s/ Vincent Sweeney
       -------------                      -------------------
                                      Name:   Vincent Sweeney
                                      Title:  Plan Administrator


                                       12