As filed with the Securities and Exchange Commission on March 31, 2006

                                                Registration No. _______________

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                   ----------
                                    FORM S-3
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                   ----------
                             SIGA Technologies, Inc.
             (Exact name of registrant as specified in its charter)

          Delaware                                      13-3864870
(State or Other Jurisdiction of            (I.R.S. Employer identification No.)
Incorporation or Organization)

                              420 Lexington Avenue
                                    Suite 408
                            New York, New York 10170
                            (212) 672-9100 (Address,
                             including zip code, and
                    telephone number, including area code, of
                    Registrant's principal executive office)
                                   ----------
                               Thomas N. Konatich
                             Chief Financial Officer
                             SIGA Technologies, Inc.
                              420 Lexington Avenue
                                    Suite 408
                            New York, New York 10170
                                 (212) 672-9100
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)
                                   ----------

                                    COPY TO:

                            Thomas E. Constance, Esq.
                       Kramer Levin Naftalis & Frankel LLP
                           1177 Avenue of the Americas
                            New York, New York 10036
                                 (212) 715-9100

      Approximate date of commencement of proposed sale to the public: From time
to time as determined by the Selling Stockholders.

      If the only  securities  being  registered  on this Form are being offered
pursuant to dividend or interest  reinvestment plans, please check the following
box. |_|



      If any of the securities  being  registered on this Form are to be offered
on a delayed or continuous  basis  pursuant to Rule 415 under the Securities Act
of 1933,  other than  securities  offered only in  connection  with  dividend or
interest reinvestment plans, check the following box. |X|

      If this Form is filed to register  additional  securities  for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration  statement  number  of the  earlier
effective registration statement for the same offering. |_|

      If this Form is a  post-effective  amendment filed pursuant to Rule 462(c)
under the  Securities  Act,  check the following box and list the Securities Act
registration  statement number of the earlier effective  registration  statement
for the same offering. |_|

      If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. |_|

                         CALCULATION OF REGISTRATION FEE



-------------------------------------------------------------------------------------------------------------
                                                   Proposed Maximum     Proposed Maximum
Title of Each Class of            Amount to be      Offering Price     Aggregate Offering      Amount of
Securities to be Registered        Registered          Per Unit              Price          Registration Fee
-------------------------------------------------------------------------------------------------------------
                                                                                      
common stock, par value
$.0001 per share..............      2,000,000 (1)        $1.22 (2)          $2,430,000            $260.01
-------------------------------------------------------------------------------------------------------------


(1)   Pursuant to Rule 416 under the  Securities  Act of 1933, as amended,  this
      registration  statement also covers such indeterminate number of shares of
      common stock as may be required to prevent  dilution  resulting from stock
      splits,  stock  dividends or similar  events.  This number  represents the
      aggregate of 2,000,000  shares  underlying  additional  investment  rights
      issued pursuant to a securities purchase agreement dated November 2, 2005,
      between SIGA and certain investors thereto. In addition, this registration
      covers  any  additional  indeterminate  number of shares of common  stock,
      which may become issuable as a result of  anti-dilution  provisions of the
      additional investment rights.

(2)   Estimated   solely  for  the  purpose  of  computing  the  amount  of  the
      registration  fee, in accordance with Rule 457(c) under the Securities Act
      of 1933, as amended.  The maximum offering price per share is $1.22, which
      was the average high and low prices for SIGA's common stock as reported on
      the NASDAQ Capital Market on March 24, 2006.

      The Registrant hereby amends this  registration  statement on such date or
dates as may be necessary to delay its effective date until the Registrant shall
file a further  amendment  which  specifically  states  that  this  registration
statement shall  thereafter  become effective in accordance with Section 8(a) of
the Securities  Act of 1933 or until this  registration  statement  shall become
effective on such date as the Commission,  acting pursuant to said Section 8(a),
may determine.



       Preliminary Prospectus, Subject to Completion, dated March 31, 2006

                                2,000,000 SHARES

                             SIGA TECHNOLOGIES, INC.

                                  COMMON STOCK

                                   ----------

      Shares of common stock of SIGA  Technologies,  Inc.  are being  offered by
this  prospectus.  The  shares  will be sold  from  time to time by the  selling
stockholders  named  in this  prospectus.  The  prices  at  which  such  selling
stockholders  may sell the shares will be  determined by the  prevailing  market
price for the shares or in  negotiated  transactions.  The  market  price of our
common stock as of the close of business  day on March 30, 2006,  was $1.429 per
share.  We will not receive any proceeds from the sale of shares of common stock
by the selling stockholders.  Our shares are traded on the NASDAQ Capital Market
under the symbol  "SIGA."  Our  principal  executive  offices are located at 420
Lexington  Avenue,  Suite 408, New York, New York 10170. Our telephone number is
(212) 672-9100.

                                   ----------

      Investing  in the  shares  involves  a  high  degree  of  risk.  For  more
information, please see "Risk Factors" beginning on page 4.

                                   ----------

      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 information in this preliminary  prospectus is not complete and may be
changed. These securities may not be sold until the registration statement filed
with the  Securities  and Exchange  Commission  is effective.  This  preliminary
prospectus  is not an offer  to sell  nor  does it seek an  offer  to buy  these
securities in any jurisdiction where the offer or sale is not permitted.

                                   ----------

                  The date of this prospectus is March 31, 2006



                                TABLE OF CONTENTS

ABOUT SIGA TECHNOLOGIES, INC...................................................1

RISK FACTORS...................................................................6

ABOUT THIS PROSPECTUS.........................................................14

FORWARD-LOOKING STATEMENTS....................................................14

USE OF PROCEEDS...............................................................15

SELLING STOCKHOLDERS..........................................................16

PLAN OF DISTRIBUTION..........................................................17

LEGAL MATTERS.................................................................19

EXPERTS.......................................................................19

COMMISSION'S POSITION ON INDEMNIFICATION FOR SECURITIES ACT LIABILITIES.......19

ADDITIONAL INFORMATION........................................................19

INCORPORATION BY REFERENCE....................................................20

PART II - INFORMATION NOT REQUIRED IN PROSPECTUS..............................21

SIGNATURES....................................................................23

EXHIBIT INDEX.................................................................25



                          ABOUT SIGA TECHNOLOGIES, INC.

      We  are  a   biotechnology   company  aiming  to  discover,   develop  and
commercialize  novel  anti-infectives,  antibiotics  and  vaccines  for  serious
infectious  diseases,  including  products for use in defense against biological
warfare agents such as Smallpox and Arenaviruses  (hemorrhagic fevers). Our lead
product,  SIGA-246,  is an orally administered  anti-viral drug that targets the
smallpox virus. In December 2005 the Food and Drug Administration (FDA) accepted
our  Investigational  New Drug (IND)  application  for  SIGA-246 and granted the
program  "Fast-Track" status. Our anti-viral programs are designed to prevent or
limit the replication of the viral pathogen.  Our  anti-infectives  programs are
aimed  at the  increasingly  serious  problem  of drug  resistance.  We are also
developing a technology for the mucosal delivery of our vaccines which may allow
the  vaccines to activate the immune  system at the mucus lined  surfaces of the
body -- the mouth, the nose, the lungs and the  gastrointestinal  and urogenital
tracts -- the sites of entry for most infectious agents.

                     Product Candidates and Market Potential

                SIGA Biological Warfare Defense Product Portfolio

Anti-Smallpox  Drug:  Smallpox  virus is classified as a Category A agent by the
Center for Disease  Control and  Prevention  (CDC) and is considered  one of the
most  significant  threats  for  use as a  biowarfare  agent.  While  deliberate
introduction of any pathogenic  agent would be  devastating,  we believe the one
that holds the greatest  potential  for harming the general U.S.  population  is
Smallpox.  At present there is no effective  drug with which to treat or prevent
Smallpox  infections.  To  address  this  serious  risk,  SIGA  scientists  have
identified a lead drug candidate,  SIGA-246,  which inhibits  vaccinia,  cowpox,
ectromelia  (mousepox),  monkeypox,  camelpox,  and variola  replication in cell
culture but not other  unrelated  viruses.  Given the safety  concerns  with the
current smallpox vaccine, there should be several uses for an effective smallpox
antiviral drug:  prophylactically,  to protect the non-immune who are at risk to
exposure;  therapeutically,  to  prevent  disease  or death in those  exposed to
smallpox;  and lastly,  as an adjunct treatment to the  immunocompromised.  SIGA
scientists  are also working on several other  smallpox drug targets,  including
the  viral  proteinases,  to  develop  additional  drug  candidates  for  use in
combination  therapy if necessary.  In December  2005,  the FDA approved our IND
application  for SIGA-246.  We plan to start Phase I clinical trials in 2006, to
evaluate the safety and  tolerability of single  escalating doses of SIGA-246 in
healthy  volunteers.  The  Phase  I  human  trials  will  be  performed  at  the
Bio-defense  Clinical  Research Branch of the National  Institute of Allergy and
Infectious Diseases (NIAID),  which is part of the federal government's National
Institutes of Health (NIH).  The primary  objective of the initial study will be
to evaluate the safety and tolerability of single  escalating doses of SIGA-246.
In 2005, the drug demonstrated  significant antiviral activity in various animal
models of poxvirus disease,  including the complete  protection of golden ground
squirrels from lethal doses of monkeypox virus.

      Anti-Arenavirus Drug: Arenaviruses are hemorrhagic fever viruses that have
been  classified as Category A agents by the CDC due to the great risk that they
pose to  public  health  and  national  safety.  Among  the  Category  A viruses
recognized by the CDC, there are four  hemorrhagic  fever  arenaviruses  (Junin,
Machupo,  Guanarito  and  Sabia  viruses)  for which  there are no FDA  approved
treatments  available.  In order  to meet  this  threat,  SIGA  scientists  have
identified a lead drug candidate,  ST-294,  which has  demonstrated  significant
antiviral  activity in cell culture assays against  arenavirus  pathogens.  SIGA
also  has  earlier  stage  programs  against  other  hemorrhagic  fever  viruses
including Lassa virus,  Lymphocytic  choriomeningitis virus (LCMV), and Ebola in
development.  We  believe  that the  availability  of  hemorrhagic  fever  virus
antiviral  drugs will address  national and global security needs by acting as a
significant  deterrent and defense against the use of arenaviruses as weapons of
bioterrorism.

      Bacterial  Commensal  Vectors:  Our scientists have developed methods that
allow  essentially  any gene  sequence to be expressed in Generally  Regarded As
Safe (GRAS) gram-positive  bacteria, with the foreign protein being displayed on
the  surface  of the live  recombinant  organisms.  Since  these  organisms  are
inexpensive to grow and are very stable, this technology affords the possibility
of rapidly producing live recombinant vaccines against any variety of biological
agents  that might be  encountered,  such as  Bacillus  anthracis  (anthrax)  or
Smallpox. SIGA scientists are working to develop an alternative vaccine with


                                       1


improved  safety  for use in  preventing  human  disease  caused  by  pathogenic
orthopoxviruses  such as variola virus. To accomplish this goal we are utilizing
our  newly-developed BCV (bacterial  commensal vector) technology.  BCV utilizes
gram-positive  commensal bacteria, such as Streptococcus gordonii, (S. Gordonii)
to  express  heterologous  antigens  of  interest,  either in  secreted  form or
attached to its external  surface.  Phase I human clinical  trials indicate that
this S.  gordonii  strain  is safe and  well-tolerated  in  humans.  In  several
different animal model systems S. gordonii has been shown to efficiently express
various antigens and elicit protective immune responses  (cellular,  humoral and
mucosal).  We believe that the delivery of selected  vaccinia virus antigens via
this live bacterial  vector system will provide an effective and safe method for
prevention of smallpox in humans.

      Surface  Protein  Expression   (SPEX/PLEX)  System:  Our  scientists  have
harnessed the protein expression  pathways of gram-positive  bacteria and turned
them into  protein  production  factories.  Using our  proprietary  SPEX or PLEX
systems,  we can produce  foreign  proteins at high levels in the laboratory for
use  in  subunit  vaccine   formulations  or  other  therapeutic   applications.
Furthermore,  we can envision engineering these bacteria to colonize the mucosal
surfaces of soldiers and/or civilians and secrete  therapeutic  molecules - e.g.
anti-toxins that protect against aerosolized botulism toxin.

      Antibiotics:  To combat the problems  associated with emerging  antibiotic
resistance, our scientists are developing drugs designed to address a new target
- the  bacterial  adhesion  organelles.  Specifically,  by using  novel  enzymes
required for the transport  and/or  assembly of the proteins and structures that
bacteria require for adhesion or colonization,  we are developing new classes of
broad  spectrum  antibiotics.  This may prove  invaluable  in  providing  prompt
treatment to individuals  encountering an unknown bacterial  pathogen in the air
or food supply.

                     Market for Biological Defense Programs

      The Department of Homeland Security (the "DHS")  appropriation bill signed
by  President  Bush on October 1, 2003 created a  discretionary  reserve of $5.6
billion   to   fund   Project    BioShield    for   a   period   of   10   years
(www.aamc.org/advocacy/library/laborhhs/labor0022.htm).   $3.4  billion  may  be
obligated  during the first 5 years of the bill,  and was included in the United
States     government's     budgets     for     fiscal     2004     and     2005
(www.whitehouse.gov/omb/budget/fy2006/tables.html).  The  remainder  is reserved
for the last 5 years of the bill.  Project BioShield was introduced to encourage
pharmaceutical   and   biotechnology    companies   to   develop    bioterrorism
countermeasures.  One of the major  concerns in the field of biological  warfare
agents is  Smallpox -  although  declared  extinct  in 1980 by the World  Health
Organization  (WHO),  there is a threat that a rogue nation or a terrorist group
may have an illegal inventory of the virus that causes Smallpox.  The only legal
inventories of the virus are held under  extremely  tight security at the CDC in
Atlanta,  Georgia and at a laboratory in Russia. As a result of this threat, the
U.S.  government has announced its intent to make  significant  expenditures  on
finding a way to  counteract  the virus if turned  loose by  terrorists  or on a
battlefield.  The Congressional  Budget Office (the "CBO") reported that the DHS
projects the  acquisition  of 60 million  doses of new Smallpox  vaccines over a
three year period, commencing in 2005. Further the CBO reports that the DHS will
spend an  additional  $1 billion to replace  expired  stocks in  2007-2013.  The
market  opportunity  for our biological  warfare  defense  products has not been
quantified as yet beyond the potential to obtain a share of the approximately $9
billion the federal  government is committing to support  research in the coming
year.

      The FDA amended its regulations,  effective June 30, 2002, so that certain
new drug and  biological  products  used to reduce or prevent  the  toxicity  of
chemical,  biological,  radiological,  or nuclear substances may be approved for
use in humans based on evidence of  effectiveness  derived only from appropriate
animal studies and any additional  supporting  data. We believe that this change
could  make it  possible  for us to have our  products  which  have been  proven
effective in animal  studies to be approved  for sale within a relatively  short
time.

                       SIGA Antibiotics Product Portfolio

      Our anti-infectives  program is targeted principally toward drug-resistant
bacteria and hospital-acquired infections.  According to estimates from the CDC,
approximately two million hospital-acquired


                                       2


infections occur each year in the United States. Our anti-infectives  approaches
aim to block the  ability of bacteria to attach to and  colonize  human  tissue,
thereby  blocking  infection  at the first stage in the  infection  process.  By
comparison,  antibiotics  available  today act by  interfering  with  either the
structure  or the  metabolism  of a  bacterial  cell,  affecting  its ability to
survive  and  to  reproduce.  No  currently  available  antibiotics  target  the
attachment of a bacterium to its target  tissue.  We believe that, by preventing
attachment,  the bacteria should be readily cleared by the body's immune system.
SIGA  has   Gram-positive,   Gram-negative   and   broad   spectrum   antibiotic
technologies.

                        SIGA Antivirals Product Portfolio

      SIGA currently has the following  antiviral  programs which are in various
stages of development  ranging from initial research and screening to initiation
of Phase I human  clinical  trials:  Smallpox  antiviral,  New World  Arenavirus
antiviral,   Old  World  Arenavirus  antiviral,   Filovirus  (Ebola  &  Marburg)
antivirals,  Dengue Fever virus antiviral, and Bunyavirus antivirals.  Currently
there are no approved antivirals available against any of these viruses.

                       Market for Anti-infective Programs

      There are currently  approximately  83 million  prescriptions  written for
antibiotics annually in the U.S (www.iatrogenic.org/library/antibioticlib.html).
and it is  estimated  that  the  worldwide  market  for  antibiotics  was  worth
approximately  23.7 billion in 2004  (www.pharmaprojectsplus.com).  Although our
products are too early in development  to make accurate  assessments of how well
they might  compete,  if  successfully  developed  and  marketed  against  other
products  currently  existing or in  development  at this time,  the  successful
capture of even a  relatively  small  global  market share could lead to a large
dollar volume of sales.  Some of the antivirals  that SIGA is developing are for
biowarfare  agents and the market for that area is currently  unknown,  however,
there is funding  available to purchase these drugs in Project Bioshield as well
as through the Department of Defense.  Markets for the other antiviral  programs
at SIGA vary widely  depending on the virus and where they are endemic.  Each of
these programs will be assessed on an individual  basis as they approach the New
Drug Application stage.

                                   Technology

                      Antiviral Technology: Two Approaches

      SIGA has two approaches to the discovery and  development of new antiviral
compounds:  rational  drug  design  and  high-throughput  screening  (HTS).  For
rational  drug design SIGA applies  advanced  receptor  structure-based  Virtual
Ligand Screening technology for ligand/inhibitor  discovery. The analysis of the
structure reveals potentially  "drugable"  pockets.  The technology allows us to
utilize the  three-dimensional  structure of the target receptor to screen large
virtual  compound  collections  as well as databases of  commercially  available
compounds and prioritize them for subsequent experimental  validation.  Rational
drug design is also used to develop  structure  activity  relationships and lead
optimization.

      For HTS SIGA uses whole cell virus  inhibition  assays,  pseudotype  virus
inhibition  assays,  as  well  as  validated  target  biochemical  assays.  SIGA
currently  has a  200,000  small  molecule  compound  library  in-house  that is
utilized for screening in these various  assays.  This strategy  allows for both
target  specific  and  target  neutral  screening  and  identification  of novel
antiviral  compounds.  Compounds  are also screened for toxicity in various cell
lines to develop a therapeutic  index (TI) which is the  concentration  that the
compound is toxic to 50% of the cells  (CC50)  divided by the  concentration  of
compound required to inhibit 50% of the virus (EC50) (TI= CC50/EC50).  Once hits
are identified with an acceptable TI they are selected for chemical optimization
and proceed in to the antiviral drug development pipeline.


                                       3


           Vaccine Technologies: Mucosal Immunity and Vaccine Delivery

      Using  proprietary   technology   licensed  from  Rockefeller   University
(Rockefeller),  SIGA is developing specific commensal bacteria ("commensals") as
a means to deliver  mucosal  vaccines.  Commensals  are harmless  bacteria  that
naturally  occupy the  body's  surfaces  with  different  commensals  inhabiting
different  surfaces,  particularly the mucosal surfaces.  Our vaccine candidates
use  genetically  engineered  commensals  to deliver  antigens  for a variety of
pathogens to the mucosal  immune  system.  When  administered,  the  genetically
engineered commensals colonize the mucosal surface and replicate.  By activating
a local mucosal immune response,  our vaccine candidates are designed to prevent
infection  and  disease  at the  earliest  possible  stage,  as  opposed to most
conventional  vaccines  which are  designed to act after  infection  has already
occurred.

      Our commensal vaccine candidates use Gram-positive  bacteria.  Rockefeller
scientists  have  identified  a  protein  region  that is used by  Gram-positive
bacteria to anchor  proteins  to their  surfaces.  We are using the  proprietary
technology  licensed from  Rockefeller to combine  antigens from a wide range of
infectious organisms,  both viral and bacterial, with the surface protein anchor
region of a variety of commensal organisms. By combining a specific antigen with
a specific  commensal,  vaccines may be tailored to both the target pathogen and
its mucosal point of entry.

      To target an immune response to a particular  mucosal surface, a commensal
vaccine would employ a commensal  organism that naturally inhabits that surface.
For example,  vaccines  targeting  sexually  transmitted  diseases  might employ
Lactobacillus  acidophilus,  a commensal colonizing the female urogenital tract.
Vaccines targeting gastrointestinal diseases could employ Lactobacillus casei, a
commensal  colonizing the  gastrointestinal  tract.  We have  conducted  initial
experiments  using S.  gordonii,  a commensal that colonizes the oral cavity and
which may be used in vaccines  targeting  pathogens that enter through the upper
respiratory tract, such as the influenza virus.

      By using  an  antigen  unique  to a given  pathogen,  the  technology  may
potentially  be applied to any  infectious  agent that enters the body through a
mucosal  surface.  Our scientists have expressed and anchored a variety of viral
and bacterial  antigens on the outside of S. gordonii,  including the M6 protein
from  group A  streptococcus,  a group  of  organisms  that  causes  a range  of
diseases,  including strep throat,  necrotizing fasciitis,  impetigo and scarlet
fever. In addition, proteins from other infectious agents, such as HIV and human
papilloma  virus have also been  expressed  using this  system.  We believe this
technology  will enable the  expression of most  antigens  regardless of size or
shape. In animal studies, we have shown that the administration of a genetically
engineered S. gordonii  vaccine  prototype  induces both a local mucosal  immune
response and a systemic immune response.

      We believe that mucosal vaccines developed using our proprietary commensal
delivery technology could provide a number of advantages, including:

o     More complete protection than conventional  vaccines:  Mucosal vaccines in
      general may be more effective than conventional  parenteral vaccines,  due
      to  mucosal  vaccines'  ability  to  produce  both a  systemic  and  local
      (mucosal) immune response.

o     Safety advantage over other live vectors: A number of bacterial  pathogens
      have been genetically rendered less infectious, or attenuated,  for use as
      live  vaccine  vectors.  Commensals,  by  virtue  of  their  substantially
      harmless  nature,  may  offer a safer  delivery  vehicle  without  fear of
      genetic   reversion  to  the  infectious   state  inherent  in  attenuated
      pathogens.

o     Non-injection    administration:    Oral,   nasal,   rectal   or   vaginal
      administration of the vaccine  eliminates the need for painful  injections
      with their potential adverse reactions.

o     Potential  for  combined   vaccine   delivery:   The  Children's   Vaccine
      Initiative,   a  worldwide  effort  to  improve  vaccination  of  children
      sponsored by the WHO, has called for the development of combined vaccines,
      specifically to reduce the number of needle sticks per child, by combining
      several  vaccines into one injection,  thereby  increasing  compliance and
      decreasing disease. We believe our commensal delivery technology can be an
      effective method of delivery of multi-component vaccines within a


                                       4


      single  commensal  organism  that  address  multiple  diseases or diseases
      caused by multiple strains of an infectious agent.

o     Eliminating need for  refrigeration:  One of the problems  confronting the
      effective delivery of parenteral vaccines is the need for refrigeration at
      all stages prior to injection. The stability of the commensal organisms in
      a  freeze-dried  state would,  for the most part,  eliminate  the need for
      special climate conditions,  a critical consideration,  especially for the
      delivery of vaccines in developing countries.

o     Low  cost  production:   By  using  a  live  bacterial  vector,  extensive
      downstream processing is eliminated,  leading to considerable cost savings
      in the production of the vaccine.  The potential for  eliminating the need
      for refrigeration  would add considerably to these savings by reducing the
      costs inherent in refrigeration for vaccine delivery.

              Surface Protein Expression Systems ("SPEX" & "PLEX")

      The ability to overproduce many bacterial and human proteins has been made
possible through the use of recombinant DNA technology.  The introduction of DNA
molecules  into  Escherichia  coli (E.  coli)  has been the  method of choice to
express  a  variety  of  gene  products,   because  of  this  bacterium's  rapid
reproduction and well-understood  genetics. Yet, despite the development of many
efficient E.  coli-based  gene expression  systems,  the most important  concern
continues  to  be  associated  with  subsequent  purification  of  the  product.
Recombinant  proteins  produced in this  manner do not  readily  cross E. coli's
outer  membrane,  and as a result,  proteins must be purified from the bacterial
cytoplasm or  periplasmic  space.  Purification  of proteins from these cellular
compartments can be very difficult.  Frequently encountered problems include low
product yields,  contamination  with potentially  toxic cellular material (i.e.,
endotoxin)  and the formation of large amounts of partially  folded  polypeptide
chains in non-active aggregates termed inclusion bodies.

      To overcome these  problems,  we have taken  advantage of our knowledge of
Gram-positive  bacterial protein expression and anchoring pathways. This pathway
has  evolved to handle the  transport  of surface  proteins  that vary widely in
size,  structure and function.  Modifying the approach used to create  bacterial
commensal  mucosal  vaccines,  we  have  developed  methods  which,  instead  of
anchoring the foreign  protein to the surface of the  recombinant  Gram-positive
bacteria,  result in it being secreted into the  surrounding  medium in a manner
which  is  readily  amenable  to  simple  batch  purification.  We  believe  the
advantages  of this  approach  include the ease and lower cost of  Gram-positive
bacterial  growth,  the likelihood  that secreted  recombinant  proteins will be
folded properly, and the ability to purify recombinant proteins from the culture
medium  without having to disrupt the bacterial  cells and  liberating  cellular
contaminants.  Gram-positive  bacteria  may be grown simply in scales from those
required  for  laboratory  research up to  commercial  mass  production.  Recent
developments in the construction of these recombinant  bacteria have resulted in
a plasmid-based  expression system (PLEX), in which engineered  genetic elements
(plasmids)  are cloned into  commensal  bacteria  for protein  production.  This
system  allows for higher  protein  production  levels  than the  original  SPEX
constructs.  In  addition,  the PLEX and SPEX  systems  may be used in  concert,
enabling  greater  flexibility  in protein  secretion  for  purification  or for
surface expression of multiple proteins - e.g. for  multi-component  combination
vaccines.


                                       5


                                  RISK FACTORS

      Investing  in our common  stock  involves a high  degree of risk,  and you
should be able to bear  losing  your  entire  investment.  You should  carefully
consider the risks presented by the following factors.

      This prospectus contains forward-looking  statements and other prospective
information  relating to future  events.  These  forward-looking  statements and
other  information are subject to risks and  uncertainties  that could cause our
actual results to differ  materially  from our  historical  results or currently
anticipated results including the following:

We have  incurred  operating  losses since our inception and expect to incur net
losses and negative cash flow for the foreseeable future.

      We incurred net losses of approximately  $2.3 million,  $9.4 million,  and
$5.3  million  for  the  years  ended   December  31,  2005,   2004,  and  2003,
respectively.  As of December 31, 2005, 2004 and 2003, our  accumulated  deficit
was approximately $46.5 million, $44.2 million and $34.8 million,  respectively.
We expect to continue to incur significant operating expenditures.  We will need
to generate significant revenues to achieve and maintain profitability.

      We  cannot  guarantee  that  we  will  achieve  sufficient   revenues  for
profitability.  Even if we do achieve profitability, we cannot guarantee that we
can sustain or increase  profitability  on a  quarterly  or annual  basis in the
future.  If revenues grow slower than we  anticipate,  or if operating  expenses
exceed our  expectations or cannot be adjusted  accordingly,  then our business,
results of operations, financial condition and cash flows will be materially and
adversely  affected.  Because our strategy might include  acquisitions  of other
businesses,  acquisition  expenses and any cash used to make these  acquisitions
will reduce our available cash.

Our business will suffer if we are unable to raise additional equity funding.

      We  continue to be  dependent  on our ability to raise money in the equity
markets. There is no guarantee that we will continue to be successful in raising
such funds. If we are unable to raise additional  equity funds, we may be forced
to  discontinue  or cease  certain  operations.  We  currently  have  sufficient
operating  capital to finance our  operations  beyond March 31, 2007. Our annual
operating  needs  vary from year to year  depending  upon the  amount of revenue
generated  through  grants and licenses and the amount of projects we undertake,
as well as the amount of resources we expend,  in connection  with  acquisitions
all of which may  materially  differ from year to year and may adversely  affect
our business.

Our stock  price is, and we expect it to remain,  volatile,  which  could  limit
investors' ability to sell stock at a profit.

      The  volatile  price of our stock  makes it  difficult  for  investors  to
predict the value of their  investment,  to sell shares at a profit at any given
time, or to plan purchases and sales in advance. A variety of factors may affect
the market price of our common stock. These include, but are not limited to:

o     publicity  regarding  actual or  potential  clinical  results  relating to
      products under development by our competitors or us;

o     delay or failure in initiating,  completing or analyzing  pre-clinical  or
      clinical trials or the unsatisfactory design or results of these trials;

o     achievement or rejection of regulatory approvals by our competitors or us;

o     announcements of technological  innovations or new commercial  products by
      our competitors or us;

o     developments concerning proprietary rights, including patents;

o     developments concerning our collaborations;


                                       6


o     regulatory developments in the United States and foreign countries;

o     economic or other crises and other external factors;

o     period-to-period  fluctuations  in  our  revenues  and  other  results  of
      operations;

o     changes in financial estimates by securities analysts; and

o     sales and short selling activity of our common stock.

      Additionally,  because there is not a high volume of trading in our stock,
any information about SIGA in the media may result in significant  volatility in
our stock price.

      We will not be able to control many of these factors,  and we believe that
period-to-period  comparisons of our financial  results will not  necessarily be
indicative of our future performance.

      In addition, the stock market in general, and the market for biotechnology
companies in particular,  has experienced  extreme price and volume fluctuations
that may have been unrelated or disproportionate to the operating performance of
individual companies. These broad market and industry factors may seriously harm
the market price of our common stock, regardless of our operating performance.

We are in various stages of product development and there can be no assurance of
successful commercialization.

      In general, our research and development programs are at an early stage of
development.  To obtain FDA approval for our biological warfare defense products
we will be required to perform  two animal  models and provide  animal and human
safety data. Our other products will be subject to the approval guidelines under
FDA  regulatory  requirements  which  include a number of phases of  testing  in
humans.

      The FDA has not approved any of our biopharmaceutical  product candidates.
Any drug candidates developed by us will require significant additional research
and development efforts,  including extensive  pre-clinical and clinical testing
and  regulatory  approval,  prior to  commercial  sale.  We  cannot  be sure our
approach to drug discovery  will be effective or will result in the  development
of any drug.  We cannot  expect that any drugs  resulting  from our research and
development efforts will be commercially available for many years, if at all.

      We have limited experience in conducting pre-clinical testing and clinical
trials. Even if we receive initially positive  pre-clinical or clinical results,
such  results do not mean that  similar  results  will be  obtained in the later
stages of drug  development,  such as additional  pre-clinical  testing or human
clinical trials.  All of our potential drug candidates are prone to the risks of
failure  inherent  in   pharmaceutical   product   development,   including  the
possibility that none of our drug candidates will or can:

     be safe, non-toxic and effective;

     otherwise meet applicable regulatory standards;

     receive the necessary regulatory approvals;

     develop into commercially viable drugs;

     be manufactured or produced economically and on a large scale;

     be successfully marketed;

     be reimbursed by government and private insurers; and

     achieve customer acceptance.

      In  addition,  third  parties  may  preclude us from  marketing  our drugs
through  enforcement  of their  proprietary  rights that we are not aware of, or
third parties may succeed in marketing equivalent or superior


                                       7


drug products. Our failure to develop safe, commercially viable drugs would have
a material  adverse effect on our business,  financial  condition and results of
operations.

Most of our immediately  foreseeable  future revenues are contingent upon grants
and contracts from the United States  government and  collaborative  and license
agreements and we may not achieve  sufficient  revenues from these agreements to
attain profitability.

      Until and unless we successfully  make a product,  our ability to generate
revenues  will  largely   depend  on  our  ability  to  enter  into   additional
collaborative  agreements,  strategic alliances,  research grants, contracts and
license  agreements  with third parties and maintain the agreements we currently
have in place.  Substantially  all of our revenues for the years ended  December
31, 2005,  2004 and 2003,  respectively,  were derived from revenues  related to
grants,  contracts and license  agreements.  Our current revenue is derived from
contract  work  being  performed  for the NIH under two major  grants  which are
scheduled to expire in September  2006 and  contracts  with the U.S.  Army which
expire in September  2006 and December 2007.  These  agreements are for specific
work to be  performed  under the  agreements  and could only be  canceled by the
other party thereto for non-performance.  We may not earn significant  milestone
payments under our existing  collaborative  agreements  until our  collaborators
have  advanced  products  into  clinical  testing,  which may not occur for many
years, if at all.

      We have material agreements with the following collaborators:

      o     National  Institutes of Health.  Under our  collaborative  agreement
            with the NIH we have  received  SBIR Grants  totaling  approximately
            $11.1 million in 2004.  The term of these grants expire in September
            2006.  We are paid as the work is performed and the agreement can be
            cancelled for non-performance. We also have an agreement whereby the
            NIH is required to conduct  and pay for the  clinical  trials of our
            strep vaccine  product  through  phase II human trials.  The NIH can
            terminate the agreement on 60 days written notice. If terminated, we
            receive copies of all data, reports and other information related to
            the trials.  If terminated,  we would have to find another source of
            funds to continue  to conduct the trials.  We are current in all our
            obligations under our agreements.

      o     United  States  Army  Medical  Research  and  Material  Command.  In
            September  2005 we entered into a $3.2  million,  one year  contract
            with the USAMRMC.  The agreement,  for the rapid  identification and
            treatment of anti-viral diseases,  is funded through the USAF. It is
            anticipated  that our efforts will aid the USAF  Special  Operations
            Command in its use of  computational  biology to design and  develop
            specific  countermeasures  against biological threat agents Smallpox
            and  Adenovirus.  We are  current in all our  obligations  under our
            agreement.

      o     Saint Louis  University.  On September  1, 2005,  we entered into an
            agreement with Saint Louis University for the continued  development
            of one of our Smallpox  drugs.  The agreement is funded  through the
            NIH.  Under the  agreement,  SIGA will  receive  approximately  $1.0
            million  during the term of  September 1, 2005 to February 28, 2006.
            We are current in all our obligations under our agreement.

      o     United  States  Army  Medical  Research  Acquisition   Activity.  In
            December  2002, we entered into a four year contract with USAMRAA to
            develop  a drug  to  treat  Smallpox.  We  are  current  in all  our
            obligations under our agreement.

      o     Rockefeller  University.  The term of our agreement with Rockefeller
            is for the duration of the patents and a number of pending  patents.
            As we do not  currently  know  when any  patents  pending  or future
            patents will expire, we cannot at this time  definitively  determine
            the term of this agreement.  The agreement can be terminated earlier
            if we are in breach of the  provisions  of the  agreement and do not
            cure the breach in the allowed  cure  period.  We are current in all
            obligations under the contract.


                                       8


      o     Oregon State  University.  OSU is a signatory of our agreement  with
            Rockefeller.  The term of this  agreement is for the duration of the
            patents and a number of pending patents. As we do not currently know
            when any patents pending or future patents will expire, we cannot at
            this time  definitively  determine the term of this  agreement.  The
            agreement  can be  terminated  earlier  if we are in  breach  of the
            provisions  of the  agreement  and do not  cure  the  breach  in the
            allowed cure  period.  We are current in all  obligations  under the
            contract. We have also entered into a subcontract agreement with OSU
            for us to  perform  work  under a grant  OSU has from  the NIH.  The
            subcontract  agreement was renewable  annually and the current terms
            expired on August 31, 2003.  Work on this agreement was completed in
            2003.

      o     Washington  University.  We have licensed  certain  technology  from
            Washington under a non-exclusive license agreement.  The term of our
            agreement  with  Washington is for the duration of the patents and a
            number of  pending  patents.  As we do not  currently  know when any
            patents  pending or future  patents will  expire,  we cannot at this
            time  definitively  determine  the  term  of  this  agreement.   The
            agreement  cannot be  terminated  unless we fail to pay our share of
            the  joint  patent  costs  for  the  technology  licensed.  We  have
            currently met all our obligations under this agreement.

      o     Regents of the  University of California.  We have licensed  certain
            technology from Regents under an exclusive license agreement. We are
            required  to pay minimum  royalties  under this  agreement.  We have
            currently met all our obligations under this agreement.

      o     TransTech  Pharma,  Inc.  Under  our  collaborative  agreement  with
            TransTech Pharma, a related party, TransTech Pharma is collaborating
            with  us on the  discovery,  optimization  and  development  of lead
            compounds to certain  therapeutic  agents.  We and TransTech  Pharma
            have agreed to share the costs of development and revenues generated
            from licensing and profits from any  commercialized  products sales.
            The agreement  will be in effect until  terminated by the parties or
            upon cessation of research or sales of all products  developed under
            the  agreement.  We  are  current  in  all  obligations  under  this
            agreement.

The  biopharmaceutical  market in which we  compete  and will  compete is highly
competitive.

      The  biopharmaceutical  industry is characterized by rapid and significant
technological  change.  Our  success  will  depend on our ability to develop and
apply our  technologies in the design and development of our product  candidates
and to establish  and maintain a market for our product  candidates.  There also
are many companies, both public and private,  including major pharmaceutical and
chemical  companies,  specialized  biotechnology  firms,  universities and other
research  institutions  engaged in developing  pharmaceutical  and biotechnology
products.   Many  of  these  companies  have  substantially  greater  financial,
technical,  research and development,  and human resources than us.  Competitors
may develop products or other technologies that are more effective than any that
are being  developed by us or may obtain FDA approval for products  more rapidly
than us. If we commence  commercial sales of products,  we still must compete in
the  manufacturing  and  marketing of such  products,  areas in which we have no
experience.  Many of these  companies  also have  manufacturing  facilities  and
established  marketing  capabilities  that would enable such companies to market
competing products through existing channels of distribution. Two companies with
similar profiles are VaxGen, Inc., which is developing vaccines against anthrax,
Smallpox and HIV/AIDS;  and Avant  Immunotherapeutics,  Inc.,  which has vaccine
programs for agents of biological warfare.

Because we must obtain  regulatory  clearance to test and market our products in
the United  States,  we cannot  predict  whether or when we will be permitted to
commercialize our products.

      A  pharmaceutical  product  cannot be  marketed  in the U.S.  until it has
completed  rigorous  pre-clinical  testing and clinical  trials and an extensive
regulatory  clearance process  implemented by the FDA.  Pharmaceutical  products
typically  take many years to satisfy  regulatory  requirements  and require the
expenditure  of  substantial  resources  depending on the type,  complexity  and
novelty of the product.


                                       9


      Before  commencing  clinical trials in humans,  we must submit and receive
clearance  from  the FDA by means of an IND  application.  Institutional  review
boards and the FDA oversee clinical trials and such trials:

      o     must be  conducted  in  conformance  with the FDA's good  laboratory
            practice regulations;

      o     must meet requirements for institutional review board oversight;

      o     must meet requirements for informed consent;

      o     must  meet   requirements   for  good  clinical  and   manufacturing
            practices;

      o     are subject to continuing FDA oversight;

      o     may require large numbers of test subjects; and

      o     may be suspended by us or the FDA at any time if it is believed that
            the  subjects  participating  in these  trials are being  exposed to
            unacceptable  health risks or if the FDA finds  deficiencies  in the
            IND application or the conduct of these trials.

      Before  receiving FDA clearance to market a product,  we must  demonstrate
that the product is safe and  effective on the patient  population  that will be
treated. Data we obtain from preclinical and clinical activities are susceptible
to  varying  interpretations  that  could  delay,  limit or  prevent  regulatory
clearances.  Additionally, we have limited experience in conducting and managing
the clinical trials and manufacturing  processes  necessary to obtain regulatory
clearance.

      If regulatory  clearance of a product is granted,  this  clearance will be
limited  only  to  those  states  and   conditions  for  which  the  product  is
demonstrated  through  clinical  trials  to be safe and  efficacious.  We cannot
ensure that any compound developed by us, alone or with others, will prove to be
safe and  efficacious  in  clinical  trials and will meet all of the  applicable
regulatory requirements needed to receive marketing clearance.

If our  technologies  or  those of our  collaborators  are  alleged  or found to
infringe the patents or proprietary  rights of others, we may be sued or have to
license those rights from others on unfavorable terms.

      Our commercial success will depend significantly on our ability to operate
without  infringing the patents and  proprietary  rights of third  parties.  Our
technologies, along with our licensors' and our collaborators' technologies, may
infringe  the patents or  proprietary  rights of others.  If there is an adverse
outcome  in  litigation  or an  interference  to  determine  priority  or  other
proceeding  in a court or  patent  office,  then we,  or our  collaborators  and
licensors,  could be subjected to significant  liabilities,  required to license
disputed  rights  from or to other  parties  and/or  required  to cease  using a
technology necessary to carry out research,  development and  commercialization.
At present we are unaware of any or potential  infringement  claims  against our
patent portfolio.

      The costs to establish the validity of patents,  to defend  against patent
infringement  claims of others and to assert  infringement claims against others
can be  expensive  and time  consuming,  even if the  outcome is  favorable.  An
outcome of any patent prosecution or litigation that is unfavorable to us or one
of our licensors or  collaborators  may have a material adverse effect on us. We
could incur  substantial  costs if we are required to defend ourselves in patent
suits  brought by third  parties,  if we  participate  in patent  suits  brought
against or initiated by our  licensors or  collaborators  or if we initiate such
suits. We may not have sufficient funds or resources in the event of litigation.
Additionally, we may not prevail in any such action.

      Any conflicts  resulting from third-party patent  applications and patents
could  significantly  reduce the coverage of the patents  owned,  optioned by or
licensed  to us or our  collaborators  and  limit  our  ability  or  that of our
collaborators to obtain meaningful patent  protection.  If patents are issued to
third parties that contain  competitive or conflicting claims, we, our licensors
or our collaborators may be legally  prohibited from researching,  developing or
commercializing of potential products or be required to obtain licenses to these
patents or to develop or obtain alternative technology. We, our licensors and/or
our collaborators may


                                       10


be legally prohibited from using patented technology,  may not be able to obtain
any license to the  patents  and  technologies  of third  parties on  acceptable
terms,  if at  all,  or  may  not be  able  to  obtain  or  develop  alternative
technologies.

      In addition,  like many biopharmaceutical  companies,  we may from time to
time hire scientific  personnel formerly employed by other companies involved in
one or more areas  similar to the  activities  conducted  by us. We and/or these
individuals  may be subject to allegations of trade secret  misappropriation  or
other similar claims as a result of their prior affiliations.

Our  ability  to  compete  may  decrease  if we do not  adequately  protect  our
intellectual property rights.

      Our commercial  success will depend in part on our and our  collaborators'
ability  to  obtain  and  maintain   patent   protection  for  our   proprietary
technologies,  drug targets and potential  products and to effectively  preserve
our  trade  secrets.  Because  of the  substantial  length  of time and  expense
associated  with  bringing   potential  products  through  the  development  and
regulatory  clearance  processes to reach the  marketplace,  the  pharmaceutical
industry  places  considerable  importance on obtaining  patent and trade secret
protection.  The patent positions of pharmaceutical and biotechnology  companies
can be highly  uncertain  and involve  complex legal and factual  questions.  No
consistent  policy  regarding  the  breadth of claims  allowed in  biotechnology
patents has emerged to date. Accordingly, we cannot predict the type and breadth
of claims allowed in these patents.

      We have licensed the rights to eight issued U.S.  patents and three issued
European  patents.  These patents have varying lives and they are related to the
technology licensed from Rockefeller  University for the Strep and Gram-positive
products.  We  have  one  additional  patent  application  in the  U.S.  and one
application  in Europe  relating  to this  technology.  We are joint  owner with
Washington  University of seven issued patents in the U.S. and one in Europe. In
addition,  there are four co-owned U.S. patent  applications.  These patents are
for the technology used for the Gram-negative product opportunities. We are also
exclusive owner of one U.S. patent and three U.S.  patent  applications.  One of
these U.S. patent applications relates to our DegP product opportunities.

      We also rely on copyright protection, trade secrets, know-how,  continuing
technological innovation and licensing  opportunities.  In an effort to maintain
the confidentiality and ownership of trade secrets and proprietary  information,
we  require  our  employees,  consultants  and  some  collaborators  to  execute
confidentiality  and invention  assignment  agreements  upon  commencement  of a
relationship with us. These agreements may not provide meaningful protection for
our  trade  secrets,  confidential  information  or  inventions  in the event of
unauthorized use or disclosure of such  information,  and adequate  remedies may
not exist in the event of such unauthorized use or disclosure.

We may have difficulty managing our growth.

      We expect to  experience  growth in the  number of our  employees  and the
scope of our operations.  This future growth could place a significant strain on
our  management  and  operations.  Our ability to manage this growth will depend
upon our ability to broaden our management team and our ability to attract, hire
and retain skilled employees. Our success will also depend on the ability of our
officers and key employees to continue to implement and improve our  operational
and other systems and to hire, train and manage our employees.

Our activities  involve hazardous  materials and may subject us to environmental
regulatory liabilities.

      Our biopharmaceutical research and development involves the controlled use
of hazardous and radioactive  materials and biological  waste. We are subject to
federal,  state and local laws and regulations  governing the use,  manufacture,
storage,  handling and disposal of these  materials and certain waste  products.
Although we believe that our safety  procedures  for  handling and  disposing of
these materials comply with legally prescribed standards, the risk of accidental
contamination or injury from these materials cannot be completely eliminated. In
the event of an accident, we could be held liable for


                                       11


damages,  and this  liability  could  exceed our  resources.  The  research  and
development  activities  of our company do not  produce  any  unusual  hazardous
products. We do use small amounts of 32P, 35S and 3H, which are stored, used and
disposed  of  in  accordance   with  Nuclear   Regulatory   Commission   ("NRC")
regulations.  We maintain  liability  insurance  in the amount of  approximately
$5,000,000  and we believe  this should be  sufficient  to cover any  contingent
losses.

      We  believe  that  we are in  compliance  in all  material  respects  with
applicable  environmental  laws and  regulations  and currently do not expect to
make  material  additional  capital   expenditures  for  environmental   control
facilities in the near term.  However, we may have to incur significant costs to
comply with current or future environmental laws and regulations.

Our potential products may not be acceptable in the market or eligible for third
party  reimbursement  resulting  in a negative  impact on our  future  financial
results.

      Any products  successfully  developed by us or our collaborative  partners
may  not  achieve  market  acceptance.  The  antibiotic  products  which  we are
attempting to develop will compete with a number of well-established traditional
antibiotic drugs  manufactured and marketed by major  pharmaceutical  companies.
The degree of market  acceptance  of any of our products will depend on a number
of factors, including:

      o     the  establishment and demonstration in the medical community of the
            clinical efficacy and safety of such products,

      o     the potential  advantage of such  products  over existing  treatment
            methods, and

      o     reimbursement policies of government and third-party payors.

      Physicians, patients or the medical community in general may not accept or
utilize any products  that we or our  collaborative  partners  may develop.  Our
ability to receive revenues and income with respect to drugs, if any,  developed
through the use of our technology will depend, in part, upon the extent to which
reimbursement  for the cost of such drugs  will be  available  from  third-party
payors,  such as government health  administration  authorities,  private health
care insurers,  health maintenance  organizations,  pharmacy benefits management
companies and other organizations. Third-party payors are increasingly disputing
the prices charged for pharmaceutical products. If third-party reimbursement was
not available or sufficient  to allow  profitable  price levels to be maintained
for drugs  developed by us or our  collaborative  partners,  it could  adversely
affect our business.

If our products harm people, we may experience product liability claims that may
not be covered by insurance.

      We  face an  inherent  business  risk of  exposure  to  potential  product
liability claims in the event that drugs we develop are alleged to cause adverse
effects  on  patients.  Such risk  exists  for  products  being  tested in human
clinical  trials,  as well as products  that  receive  regulatory  approval  for
commercial sale. We may seek to obtain product liability  insurance with respect
to drugs we and/or or our collaborative partners develop. However, we may not be
able to obtain such insurance.  Even if such insurance is obtainable, it may not
be  available  at a  reasonable  cost or in a  sufficient  amount to  protect us
against liability.

We may be required to perform additional  clinical trials or change the labeling
of our products if we or others  identify side effects after our products are on
the market, which could harm sales of the affected products.

      If we or others  identify  side  effects  after any of our products on the
market, or if manufacturing problems occur:

o     regulatory approval may be withdrawn;

o     reformulation  of our products,  additional  clinical  trials,  changes in
      labeling of our products may be required;


                                       12


o     changes  to  or  re-approvals  of  our  manufacturing  facilities  may  be
      required;

o     sales of the affected products may drop significantly;

o     our reputation in the marketplace may suffer; and

o     lawsuits, including class action suits, may be brought against us.

      Any of the above  occurrences  could harm or prevent sales of the affected
products  or could  increase  the  costs and  expenses  of  commercializing  and
marketing these products.

The manufacture of biotechnology  products can be a  time-consuming  and complex
process which may delay or prevent  commercialization  of our  products,  or may
prevent  our  ability  to  produce  an  adequate   volume  for  the   successful
commercialization of our products.

      Our  management  believes  that we have the  ability to acquire or produce
quantities of products  sufficient to support our present needs for research and
our  projected  needs  for  our  initial  clinical  development  programs.   The
manufacture of all of our products will be subject to current Good Manufacturing
Practices (GMP) requirements prescribed by the FDA or other standards prescribed
by the  appropriate  regulatory  agency in the  country of use.  There can be no
assurance  that  we  will be able  to  manufacture  products,  or have  products
manufactured for us, in a timely fashion at acceptable quality and prices,  that
we or third party  manufacturers  can comply with GMP, or that we or third party
manufacturers will be able to manufacture an adequate supply of product.

Healthcare  reform and  controls on  healthcare  spending may limit the price we
charge for any products and the amounts thereof that we can sell.

      The U.S.  federal  government and private insurers have considered ways to
change, and have changed,  the manner in which healthcare  services are provided
in the U.S. Potential approaches and changes in recent years include controls on
healthcare  spending and the creation of large purchasing groups. In the future,
the U.S.  government may institute  further  controls and limits on Medicare and
Medicaid spending.  These controls and limits might affect the payments we could
collect from sales of any products.  Uncertainties  regarding future  healthcare
reform and private market  practices could adversely  affect our ability to sell
any products profitably in the U.S. At present, we do not foresee any changes in
FDA regulatory policies that would adversely affect our development programs.

The future  issuance of preferred  stock may adversely  affect the rights of the
holders of our common stock.

      Our certificate of incorporation allows our Board of Directors to issue up
to  10,000,000  shares  of  preferred  stock  and  to  fix  the  voting  powers,
designations,   preferences,   rights   and   qualifications,   limitations   or
restrictions  of  these  shares  without  any  further  vote  or  action  by the
stockholders.  The rights of the holders of common stock will be subject to, and
could be adversely affected by, the rights of the holders of any preferred stock
that we may  issue  in the  future.  The  issuance  of  preferred  stock,  while
providing  desirable  flexibility in connection with possible  acquisitions  and
other corporate purposes,  could have the effect of making it more difficult for
a third party to acquire a majority of our  outstanding  voting  stock,  thereby
delaying, deferring or preventing a change in control.

Concentration of ownership of our capital stock could delay or prevent change of
control.

      Our directors,  executive officers and principal stockholders beneficially
own a significant  percentage of our common stock and preferred stock. They also
have,  through the exercise or  conversion of certain  securities,  the right to
acquire  additional  common stock. As a result,  these  stockholders,  if acting
together,  have the ability to significantly  influence the outcome of corporate
actions requiring  shareholder  approval.  Additionally,  this  concentration of
ownership  may have the effect of delaying or  preventing a change in control of
SIGA.  At December 31, 2005,  Directors,  Officers  and  principal  stockholders
beneficially owned approximately 46.0% of our stock.


                                       13


                              ABOUT THIS PROSPECTUS

      This prospectus is part of a registration statement that we filed with the
Securities and Exchange  Commission.  The prospectus relates to 1,818,182 shares
of our common  stock which may be issued  under  certain  additional  investment
right agreements and which the selling stockholders named in this prospectus may
sell from time to time.  We will not  receive  any of the  proceeds  from  these
sales.  We have agreed to pay the expenses  incurred in registering  the shares,
including legal and accounting fees.

      The shares have not been registered under the securities laws of any state
or other  jurisdiction  as of the date of this  prospectus.  Brokers  or dealers
should  confirm the existence of an exemption  from  registration  or effectuate
such registration in connection with any offer and sale of the shares.

      This  prospectus  describes  certain risk factors that you should consider
before purchasing the shares. See "Risk Factors" beginning on page 8. You should
read this prospectus  together with the additional  information  described under
the heading "Where You Can Find More Information."

                           FORWARD-LOOKING STATEMENTS

      This prospectus contains certain  "forward-looking  statements" within the
meaning of the Private  Securities  Litigation  Reform Act of 1995,  as amended,
including statements regarding the efficacy of potential products, the timelines
for bringing such products to market and the availability of funding sources for
continued development of such products.  Forward-looking statements are based on
management's  estimates,   assumptions  and  projections,  and  are  subject  to
uncertainties,  many of which are beyond the control of SIGA. Actual results may
differ  materially  from those  anticipated  in any  forward-looking  statement.
Factors  that may cause such  differences  include the risks that (a)  potential
products that appear promising to SIGA or its  collaborators  cannot be shown to
be efficacious or safe in subsequent  pre-clinical or clinical trials,  (b) SIGA
or its  collaborators  will not obtain  appropriate  or  necessary  governmental
approvals to market these or other potential products,  (c) SIGA may not be able
to obtain  anticipated  funding for its  development  projects  or other  needed
funding, (d) SIGA may not be able to secure funding from anticipated  government
contracts  and  grants,  (e) SIGA may not be able to secure or enforce  adequate
legal  protection,  including  patent  protection,  for  its  products  and  (f)
unanticipated   internal  control  deficiencies  or  weaknesses  or  ineffective
disclosure  controls and procedures.  More detailed  information  about SIGA and
risk  factors that may affect the  realization  of  forward-looking  statements,
including the forward-looking  statements in this presentation,  is set forth in
SIGA's  filings with the Securities and Exchange  Commission,  including  SIGA's
Annual Report on Form 10-K for the fiscal year ended  December 31, 2005,  and in
other  documents that SIGA has filed with the  Commission.  SIGA urges investors
and security  holders to read those documents free of charge at the Commission's
Web  site at  http://www.sec.gov.  Interested  parties  may  also  obtain  those
documents free of charge from SIGA.  Forward-looking statements speak only as of
the date they are made,  and except for our ongoing  obligations  under the U.S.
federal  securities  laws,  we undertake no  obligation  to publicly  update any
forward-looking statements whether as a result of new information, future events
or otherwise.

      Although we believe that our expectations are reasonable, we cannot assure
you that our  expectations  will prove to be correct.  Should any one or more of
these risks or uncertainties  materialize,  or should any underlying assumptions
prove incorrect, actual results may vary materially from those described in this
prospectus as anticipated, believed, estimated, expected, intended or planned.


                                       14


                                 USE OF PROCEEDS

      The net proceeds  from the sale of the shares of common stock offered will
be received by the selling stockholders. We will not receive any of the proceeds
from the sale of the shares of common stock offered by the selling stockholders.


                                       15


                              SELLING STOCKHOLDERS

      The table below sets forth information  regarding  ownership of our common
stock by the selling stockholders as of March 30, 2006, and the shares of common
stock  to be  sold  by them  under  this  prospectus.  Beneficial  ownership  is
determined in accordance  with rules of the Securities  and Exchange  Commission
and includes voting or investment  power with respect to the securities.  Except
as indicated by footnote, and subject to applicable community property laws, the
persons named in the table have sole voting and investment power with respect to
all shares of common stock shown as beneficially owned by them. The rules of the
Securities and Exchange  Commission  require that the number of shares of common
stock  outstanding  used in  calculating  the  percentage for each listed person
includes the shares of common stock underlying  warrants or options held by such
person that are  exercisable  within 60 days of March 30, 2006.  As of March 31,
2006, 26,500,648 shares of our common stock were outstanding.



                                             Securities Owned Prior to Offering               Securities Owned After Offering
                                                                        Shares of Common
                                  Shares of Common    Percent of Common   Stock Offered     Number of Shares of   Percent of Common
Name of Selling Stockholder             Stock               Stock             Hereby            Common Stock             Stock
                                                                                                          
Smithfield Fiduciary LLC (3)           500,000              1.89%             500,000                --                  0.0%
Omicron Master Trust (2)               500,000              1.89%             500,000                --                  0.0%
Iroquois Capital LP (1)                500,000              1.89%             500,000                --                  0.0%
Cranshire Capital LP (4)               500,000              1.89%             500,000                --                  0.0%


(1) Joshua Silverman has voting control and investment  decision over securities
    held by Iroquois Capital,  LP. Mr. Silverman disclaims  beneficial ownership
    of the shares held by Iroquois Capital, LP.

(2) Omicron Capital,  L.P., a Delaware limited partnership  ("Omicron Capital"),
    serves as investment  manager to Omicron  Master Trust, a trust formed under
    the  laws  of  Bermuda  ("Omicron"),   Omicron  Capital,  Inc.,  a  Delaware
    corporation  ("OCI"),  serves as general  partner of  Omicron  Capital,  and
    Winchester Global Trust Company Limited ("Winchester") serves as the trustee
    of Omicron. By reason of such relationships,  Omicron Capital and OCI may be
    deemed to share  dispositive power over the shares of our common stock owned
    by Omicron,  and  Winchester  may be deemed to share voting and  dispositive
    power over the shares of our common stock owned by Omicron. Omicron Capital,
    OCI and  Winchester  disclaim  beneficial  ownership  of such  shares of our
    common  stock.  Omicron  Capital has delegated  authority  from the board of
    directors of Winchester  regarding the portfolio  management  decisions with
    respect to the shares of common  stock owned by Omicron and, as of April 21,
    2003,  Mr.  Olivier H. Morali and Mr. Bruce T.  Bernstein,  officers of OCI,
    have  delegated  authority  from the board of directors of OCI regarding the
    portfolio management decisions of Omicron Capital with respect to the shares
    of common  stock owned by Omicron.  By reason of such  delegated  authority,
    Messrs.  Morali and Bernstein may be deemed to share  dispositive power over
    the  shares  of our  common  stock  owned by  Omicron.  Messrs.  Morali  and
    Bernstein disclaim  beneficial  ownership of such shares of our common stock
    and neither of such persons has any legal right to maintain  such  delegated
    authority.  No other person has sole or shared voting or  dispositive  power
    with respect to the shares of our common stock being offered by Omicron,  as
    those terms are used for purposes under  Regulation  13D-G of the Securities
    Exchange  Act  of  1934,  as  amended.   Omicron  and   Winchester  are  not
    "affiliates"  of one  another,  as that  term is used  for  purposes  of the
    Securities Exchange Act of 1934, as amended, or of any other person named in
    this prospectus as a selling stockholder. No person or "group" (as that term
    is used in Section 13(d) of the Securities Exchange Act of 1934, as amended,
    or the SEC's Regulation 13D-G) controls Omicron and Winchester.

(3) Highbridge  Capital  Management,  LLC is the trading  manager of  Smithfield
    Fiduciary LLC and consequently has voting control and investment  discretion
    over  securities  held by Smithfield  Fiduciary  LLC.  Glenn Dubin and Henry
    Swieca  control  Highbridge  Capital  Management,  LLC.  Each of  Highbridge
    Capital  Management,  LLC, Glenn Dubin and Henry Swieca diclaims  beneficial
    ownership of the securities held by Smithfield Fiduciary LLC.


                                       16


(4) Mitchell P. Kopin, President of Downsview Capital, Inc., the General Partner
    of  Cranshire  Capital,  L.P.  has sole  voting  and  investment  control of
    securities held by Cranshire.

      The  information  provided in the table above with  respect to the selling
stockholders has been obtained from such selling stockholders.

      The  selling  stockholders  have not within  the past three  years had any
position,  office  or  other  material  relationship  with  us  or  any  of  our
predecessors or affiliates.

      Because  the  selling  stockholders  may sell all or some  portion  of the
shares of common stock  beneficially  owned by them, only an estimate  (assuming
the selling  stockholders sell all of the shares offered hereby) can be given as
to the number of shares of common stock that will be  beneficially  owned by the
selling stockholders after this offering. In addition,  the selling stockholders
may have sold,  transferred or otherwise  disposed of, or may sell,  transfer or
otherwise  dispose of, at any time or from time to time since the dates on which
they provided the information  regarding the shares  beneficially owned by them,
all or a portion of the shares beneficially owned by them in transactions exempt
from the registration requirements of the Securities Act.

      We have filed  with the  Securities  and  Exchange  Commission,  under the
Securities  Act of 1933,  a  registration  statement  on Form S-3, of which this
prospectus  forms a part, with respect to the resale of the securities from time
to time on the NASDAQ Capital Market or in privately-negotiated transactions and
have  agreed  to  prepare  and  file  such  amendments  and  supplements  to the
registration  statement as may be necessary to keep the  registration  statement
effective  until  the  earlier  of (i) five  years  from the date on which  this
registration statement on Form S-3 becomes effective,  or (ii) the date on which
the selling stockholders have sold all of the shares of common stock.

                              PLAN OF DISTRIBUTION

      This  prospectus  covers  the sale of shares of common  stock from time to
time by the  selling  stockholders  named in the  table  above  and any of their
pledgees, donees, assignees and successors-in-interest.

The selling stockholders may, from time to time, sell any or all of their shares
of common stock on any stock exchange,  market or trading  facility on which the
shares  are traded or in private  transactions.  These  sales may be at fixed or
negotiated  prices.  The  selling  stockholders  may  use any one or more of the
following methods when selling shares:

o   ordinary brokerage  transactions and transactions in which the broker-dealer
    solicits purchasers;

o   block trades in which the  broker-dealer  will attempt to sell the shares as
    agent but may  position  and resell a portion of the block as  principal  to
    facilitate the transaction;

o   purchases by a  broker-dealer  as principal and resale by the  broker-dealer
    for its account;

o   an exchange  distribution  in  accordance  with the rules of the  applicable
    exchange;

o   privately negotiated transactions;

o   short sales;

o   through the writing or settlement of options or other hedging  transactions,
    whether through an options exchange or otherwise;

o   broker-dealers  may agree with the selling  stockholders to sell a specified
    number of such shares at a stipulated price per share; and

o   a combination of any such methods of sale.

The  selling  stockholders  may  also  sell  shares  under  Rule 144  under  the
Securities Act, if available, rather than under this prospectus.

      The selling  stockholders  may also engage in short sales against the box,
puts and calls and other  transactions  in our  securities or derivatives of our
securities and may sell or deliver shares in connection with these trades.


                                       17


      Broker-dealers  engaged by the selling  stockholders may arrange for other
brokers-dealers to participate in sales.  Broker-dealers may receive commissions
or discounts from the selling  stockholders  (or, if any  broker-dealer  acts as
agent  for the  purchaser  of  shares,  from the  purchaser)  in  amounts  to be
negotiated.  The  selling  stockholders  do not  expect  these  commissions  and
discounts to exceed what is customary in the types of transactions involved. Any
profits on the  resale of shares of common  stock by a  broker-dealer  acting as
principal might be deemed to be underwriting  discounts or commissions under the
Securities  Act.  Discounts,   concessions,   commissions  and  similar  selling
expenses,  if any, attributable to the sale of shares will be borne by a selling
stockholder.  The selling  stockholders may agree to indemnify any agent, dealer
or broker-dealer that participates in transactions involving sales of the shares
if liabilities are imposed on that person under the Securities Act.

      In connection with the sale of our common stock or interests therein,  the
selling  stockholders may enter into hedging transactions with broker-dealers or
other  financial  institutions,  which may in turn  engage in short sales of the
common stock in the course of hedging the  positions  they  assume.  The selling
stockholders  may also sell shares of our common  stock short and deliver  these
securities  to close out their  short  positions,  or loan or pledge  the common
stock to  broker-dealers  that in turn may sell these  securities.  The  selling
stockholders   may  also  enter   into   option  or  other   transactions   with
broker-dealers  or other  financial  institutions or the creation of one or more
derivative  securities which require the delivery to such broker-dealer or other
financial  institution of shares offered by this  prospectus,  which shares such
broker-dealer  or  other  financial  institution  may  resell  pursuant  to this
prospectus (as supplemented or amended to reflect such transaction).

      The selling  stockholders may from time to time pledge or grant a security
interest in some or all of the shares of common stock owned by them and, if they
default in the performance of their secured obligations, the pledgees or secured
parties  may offer and sell the  shares of common  stock from time to time under
this prospectus  after we have filed an amendment to this prospectus  under Rule
424(b)(3) or other  applicable  provision of the Securities Act of 1933 amending
the list of selling  stockholders  to include the pledgee,  transferee  or other
successors in interest as selling stockholders under this prospectus.

      The selling  stockholders  also may transfer the shares of common stock in
other circumstances, in which case the transferees, pledgees or other successors
in  interest  will  be the  selling  beneficial  owners  for  purposes  of  this
prospectus  and may sell the shares of common stock from time to time under this
prospectus  after we have  filed an  amendment  to this  prospectus  under  Rule
424(b)(3) or other  applicable  provision of the Securities Act of 1933 amending
the list of selling  stockholders  to include the pledgee,  transferee  or other
successors in interest as selling stockholders under this prospectus.

      The  selling  stockholders  and any  broker-dealers  or  agents  that  are
involved  in  selling   the  shares  of  common   stock  may  be  deemed  to  be
"underwriters"  within the meaning of the Securities Act in connection with such
sales. In such event, any commissions  received by such broker-dealers or agents
and any profit on the resale of the shares of common stock purchased by them may
be deemed to be underwriting commissions or discounts under the Securities Act.

      We are required to pay all fees and expenses  incident to the registration
of the  shares  of  common  stock.  We have  agreed  to  indemnify  the  selling
stockholders against certain losses, claims, damages and liabilities,  including
liabilities under the Securities Act.

      The selling  stockholders  have advised us that they have not entered into
any  agreements,   understandings  or  arrangements  with  any  underwriters  or
broker-dealers  regarding the sale of their shares of common stock, nor is there
an underwriter or coordinating  broker acting in connection with a proposed sale
of shares of common stock by any selling stockholder.  If we are notified by any
selling  stockholder that any material  arrangement has been entered into with a
broker-dealer for the sale of shares of common stock, if required,  we will file
a supplement to this prospectus. If the selling stockholders use this prospectus
for any  sale of the  shares  of  common  stock,  they  will be  subject  to the
prospectus delivery requirements of the Securities Act.

      The anti-manipulation  rules of Regulation M under the Securities Exchange
Act of 1934 may apply to sales of our common stock and activities of the selling
stockholders.


                                       18


                                  LEGAL MATTERS

The  validity of the shares of common stock  offered  hereby will be passed upon
for us by Kramer Levin Naftalis & Frankel LLP. Thomas E.  Constance,  a director
of SIGA,  is Chairman of Kramer Levin  Naftalis & Frankel LLP, a law firm in New
York City, which SIGA has retained to provide legal services.

                                     EXPERTS

      The financial  statements  incorporated in this prospectus by reference to
the Annual Report on Form 10-K for the year ended December 31, 2005 have been so
incorporated  in  reliance  on the  report  of  PricewaterhouseCoopers  LLP,  an
independent  registered  public  accounting firm, given on the authority of said
firm as experts in auditing and accounting.

     COMMISSION'S POSITION ON INDEMNIFICATION FOR SECURITIES ACT LIABILITIES

      Insofar as  indemnification  for liabilities  arising under the Securities
Act of 1933 may be permitted to our directors, officers and controlling persons,
we have  been  advised  that  in the  opinion  of the  Securities  and  Exchange
Commission  such  indemnification  is against  public policy as expressed in the
Securities Act and is, therefore,  unenforceable.  In the event that a claim for
indemnification  against  such  liabilities  (other  than the  payment  by us of
expenses  incurred  or paid by one of our  directors,  officers  or  controlling
persons in the successful defense of any action, suit or proceeding) is asserted
by  that  director,  officer  or  controlling  person  in  connection  with  the
securities being  registered,  we will, unless in the opinion of our counsel the
matter  has  been  settled  by  controlling  precedent,  submit  to a  court  of
appropriate  jurisdiction  the question  whether that  indemnification  by us is
against public policy as expressed in the Securities Act and will be governed by
the final adjudication of that issue.

                             ADDITIONAL INFORMATION

Government Filings.

      We file annual,  quarterly and special reports, proxy statements and other
information  with the SEC. Our SEC filings are  available to the public over the
Internet at the SEC's web site at http://www.sec.gov. You may also read and copy
any document we file at the SEC's  public  reference  room at 450 Fifth  Street,
N.W., Washington, D.C. 20549. You may obtain information on the operation of the
SEC's  public  reference  room  in  Washington,  D.C.  by  calling  the  SEC  at
1-800-SEC-0330.

      We  have  filed  with  the SEC a  registration  statement  on form  S-3 to
register the shares of common stock to be offered.  This  prospectus  is part of
that  registration  statement  and, as permitted  by the SEC's  rules,  does not
contain all the information included in the registration statement.  For further
information about us and our common stock, you should refer to that registration
statement and to the exhibits and schedules  filed as part of that  registration
statement,  as well as the documents we have incorporated by reference which are
discussed  below.  You can  review  and copy  the  registration  statement,  its
exhibits  and  schedules,  as well as the  documents  we  have  incorporated  by
reference, at the public reference facilities maintained by the SEC as described
above. The  registration  statement,  including its exhibits and schedules,  are
also available on the SEC's web site, given above.

Stock Market.

      Shares of our common stock are traded on the NASDAQ Capital Market.


                                       19


                           INCORPORATION BY REFERENCE

      The SEC allows us to incorporate by reference the information 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 an
important part of this  prospectus,  and information that we file later with the
SEC will automatically update and supersede this information.  We incorporate by
reference the documents  listed below and any further  filings made with the SEC
under  Sections  13(a),  13(c),  14 or 15(d) of the  Exchange  Act,  until  this
offering has been completed:

      o     the Annual Report on Form 10-K for the year ended December 31, 2005;

      o     the  description of our common stock  contained in our  registration
            statement on Form 8-A under  Section 12 of the Exchange  Act,  dated
            September 5, 1997,  including any amendment or reports filed for the
            purpose of updating such description; and

      o     our current  reports on Form 8-K filed on January 5, 2006,  February
            3, 2006, February 7, 2006, March 14, 2006 and March 22, 2006.

      We will furnish to any person,  including any  beneficial  owner,  to whom
this  prospectus is delivered,  without  charge,  a copy of these documents upon
written or oral request to Thomas N.  Konatich,  Chief  Financial  Officer,  420
Lexington Avenue, Suite 408, New York, New York 10170, tel. (212) 672-9100.


                                       20


                PART II - INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

      The  following  table sets forth the  estimated  costs and expenses of the
sale  and   distribution  of  the  securities  being   registered,   other  than
underwriting discounts and commissions, all of which are being borne by us.

                                                          Amount
                                                       -----------
             SEC filing fee .....................      $    260.01
             Printing Expenses ..................      $  2,000.00
             Legal fees and expenses ............      $  5,000.00
             Accounting fees and expenses .......      $  7,500.00
             Miscellaneous ......................      $    500.00
                      Total .....................      $ 15,260.01

      All of the amounts shown are  estimates  except for the fee payable to the
Securities and Exchange Commission.

Item 15. Indemnification of Directors and Officers

      Section  145 of the  Delaware  General  Corporation  Law  provides  that a
corporation may indemnify directors and officers, as well as other employees and
individuals,  against expenses (including attorneys' fees), judgments, fines and
amounts paid in settlement  actually and reasonably  incurred by any such person
in  connection  with any  threatened,  pending or  completed  actions,  suits or
proceedings  in which such person is made a party by reason of such person being
or having been a director,  officer,  employee or agent to the  Registrant.  The
Delaware  General  Corporation Law provides that Section 145 is not exclusive of
other rights to which those seeking  indemnification  may be entitled  under any
bylaw, agreement,  vote of stockholders or disinterested directors or otherwise.
Article IX of the Registrant's  Certificate of Incorporation  and Article VII of
the Registrant's  Bylaws provides for  indemnification  by the Registrant of its
directors and officers to the fullest extent  permitted by the Delaware  General
Corporation Law.

      Section  102(b)(7)  of the  Delaware  General  Corporation  Law  permits a
corporation to provide in its  certificate of  incorporation  that a director of
the  corporation  shall  not be  personally  liable  to the  corporation  or its
stockholders  for monetary  damages for breach of fiduciary  duty as a director,
except for liability (i) for any breach of the director's duty of loyalty to the
corporation or its stockholders, (ii) for acts or omissions not in good faith or
which involve  intentional  misconduct or a knowing  violation of law, (iii) for
unlawful  payments of dividends or unlawful  stock  repurchases,  redemptions or
other distributions, or (iv) for any transaction from which the director derived
an improper  personal  benefit.  The  Registrant's  Certificate of Incorporation
provides for such limitation of liability.

Item 16.  Exhibits

Exhibit No.   Description
-----------   -----------

5.1           Opinion of Kramer Levin Naftalis & Frankel LLP.

23.1          Consent of PricewaterhouseCoopers LLP.

23.2          Consent of Kramer  Levin  Naftalis & Frankel LLP  (contained  in
              the  opinion  filed as
              Exhibit 5.1 hereto).

24.1          Power of Attorney (included on the signature page of this
              Registration Statement).

Item 17.  Undertakings

(a) The undersigned registrant hereby undertakes:


                                       21


      (1) To file,  during any period in which offers or sales are being made, a
      post-effective amendment to this registration statement:

            (i) To include any  prospectus  required by section  10(a)(3) of the
            Securities Act of 1933;

            (ii) To reflect in the  prospectus any facts or events arising after
            the effective date of the registration statement (or the most recent
            post-effective  amendment  thereof)  which,  individually  or in the
            aggregate,  represent a fundamental  change in the  information  set
            forth in the registration statement.  Notwithstanding the foregoing,
            any  increase or decrease  in volume of  securities  offered (if the
            total dollar value of securities offered would not exceed that which
            was  registered)  and any deviation  from the low or high end of the
            estimated  maximum  offering  range may be  reflected in the form of
            prospectus  filed  with  the  Commission  pursuant  to  Rule  424(b)
            (ss.230.424(b) of this chapter) if, in the aggregate, the changes in
            volume and price  represent no more than a 20% change in the maximum
            aggregate   offering  price  set  forth  in  the   "Calculation   of
            Registration Fee" table in the effective registration statement;

            (iii) To include any material  information  with respect to the plan
            of  distribution  not  previously   disclosed  in  the  registration
            statement  or  any  material  change  to  such  information  in  the
            registration statement;

      (2)  That,  for  the  purpose  of  determining  any  liability  under  the
      Securities Act of 1933, each such post-effective amendment shall be deemed
      to be a new  registration  statement  relating to the  securities  offered
      therein,  and the offering of such securities at that time shall be deemed
      to be the initial bona fide offering thereof.

      (3) To remove from registration by means of a post-effective amendment any
      of the securities  being registered which remain unsold at the termination
      of the offering.:

      (4) That, for purposes of determining  any liability  under the Securities
      Act of 1933,  each filing of the  registrant's  annual report  pursuant to
      section  13(a) or section  15(d) of the  Securities  Exchange  Act of 1934
      (and, where  applicable,  each filing of an employee benefit plan's annual
      report  pursuant to section 15(d) of the Securities  Exchange Act of 1934)
      that is incorporated by reference in the  registration  statement shall be
      deemed  to be a new  registration  statement  relating  to the  securities
      offered therein, and the offering of such securities at that time shall be
      deemed to be the initial bona fide offering thereof.

(b) Insofar as indemnification  for liabilities arising under the Securities Act
may  be  permitted  to  directors,  officers  and  controlling  persons  of  the
Registrant pursuant to the foregoing  provisions,  or otherwise,  the Registrant
has been advised that in the opinion of the Securities  and Exchange  Commission
such indemnification is against public policy as expressed in the Securities Act
and is, therefore,  unenforceable. In the event that a claim for indemnification
against such  liabilities  (other than the payment by the Registrant of expenses
incurred or paid by a director,  officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director,  officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been  settled by  controlling  precedent,  submit to a court of  appropriate
jurisdiction the question whether such  indemnification  by it is against public
policy as  expressed  in the  Securities  Act and will be  governed by the final
adjudication of such issue.


                                       22


                                   SIGNATURES

      Pursuant  to  the  requirements  of  the  Securities  Act  of  1933,  SIGA
Technologies,  Inc.  certifies that it has reasonable grounds to believe that it
meets all of the  requirements  for filing on Form S-3 and has duly  caused this
registration statement to be signed on its behalf by the undersigned,  thereunto
duly authorized, in the City of New York, New York on March 30, 2006.

                                        SIGA Technologies, Inc.


                                        By:  /s/ Thomas N. Konatich
                                             -----------------------------------
                                             Name:  Thomas N. Konatich
                                             Title: Chief Financial Officer

      KNOW ALL  PERSONS BY THESE  PRESENTS,  that the persons  whose  signatures
appear below each severally  constitutes and appoints Thomas N. Konatich and his
true and lawful  attorneys-in-fact  and agents, with full powers of substitution
and  resubstitution,  for him and in his name,  place and stead,  in any and all
capacities,  to  sign  any  and  all  amendments  (including  pre-effective  and
post-effective  amendments)  to this  registration  statement  and to  sign  any
registration statement (and any post-effective  amendments) relating to the same
offering as this  registration  statement  that is to be  effective  upon filing
pursuant to Rule 462(b) under the  Securities Act of 1933, and to file the same,
with all  exhibits,  and  other  documents  in  connection  therewith,  with the
Securities and Exchange  Commission,  granting unto said  attorneys-in-fact  and
agents,  full power and authority to do and perform each and every act and thing
requisite and  necessary to be done in and about the  premises,  as fully to all
intents and  purposes as he might or could do in person,  hereby  ratifying  and
confirming all which said attorneys-in-fact and agents, or their substitute, may
lawfully do, or cause to be done by virtue hereof.

      Pursuant to the  requirements  of the  Securities Act of 1933, as amended,
this  registration  statement has been signed below by the following  persons in
the capacities and on the dates indicated.

Signature                       Title                          Date

/s/ Bernard L. Kasten           Chief Executive Officer,       March 30, 2006
---------------------------     Director
Bernard L. Kasten, M.D.

                                Chief Financial Officer        March 31, 2006
/s/ Thomas N. Konatich          (Principal Financial Officer
---------------------------     and Principal Accounting
Thomas N. Konatich              Officer)

/s/ Donald G. Drapkin
---------------------------
Donald G. Drapkin               Chairman of the Board          March 30, 2006

/s/ James J. Antal
---------------------------
James J. Antal                  Director                       March 30, 2006

/s/ Judy S. Slotkin
---------------------------
Judy S. Slotkin                 Director                       March 30, 2006

/s/ Thomas E. Constance
---------------------------
Thomas E. Constance             Director                       March 30, 2006

/s/ Adnan M. Mjalli
---------------------------
Adnan M. Mjalli, Ph.D.          Director                       March 31, 2006



                                       23


/s/ Mehmet C. Oz
---------------------------
Mehmet C. Oz                    Director                       March 30, 2006

/s/ Eric A. Rose
---------------------------
Eric A. Rose                    Director                       March 30, 2006

/s/ Paul G. Savas
---------------------------
Paul G. Savas                   Director                       March 31, 2006


---------------------------
Michael Weiner                  Director


                                       24


                                  EXHIBIT INDEX

Exhibit No.    Description
-----------    -----------

5.1            Opinion of Kramer Levin Naftalis & Frankel LLP.

23.1           Consent of PricewaterhouseCoopers LLP.

23.2           Consent of Kramer  Levin  Naftalis & Frankel LLP  (contained
               in the  opinion  filed as Exhibit 5.1 hereto).

24.1           Power of Attorney (included on the signature page of this
               Registration Statement).


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