PROSPECTUS                                    Filed Pursuant to Rule 424 (b) (3)
                                                     Registration No. 333-129756

                                3,060,000 SHARES

                             SIGA TECHNOLOGIES, INC.

                                  COMMON STOCK

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      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.  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 8.

                                   ----------

      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 December 2, 2005



                                TABLE OF CONTENTS

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

RISK FACTORS...................................................................8

ABOUT THIS PROSPECTUS.........................................................16

FORWARD-LOOKING STATEMENTS....................................................16

USE OF PROCEEDS...............................................................17

SELLING STOCKHOLDERS..........................................................18

PLAN OF DISTRIBUTION..........................................................18

LEGAL MATTERS.................................................................20

EXPERTS.......................................................................20

COMMISSION'S POSITION ON INDEMNIFICATION FOR SECURITIES ACT LIABILITIES.......20

ADDITIONAL INFORMATION........................................................21

INCORPORATION BY REFERENCE....................................................21



                          ABOUT SIGA TECHNOLOGIES, INC.

      We are a biotechnology  company,  whose primary focus is on the discovery,
development  and  commercialization  of 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  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.  These programs are designed to
block the ability of bacteria to attach to human  tissue,  the first step in the
infection process.  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: 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.

      Anti-Arenavirus Drug: Arenaviruses are hemorrhagic fever viruses that have
been  classified  as Category A agents by the  Centers  for Disease  Control and
Prevention  (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 United States Food and Drug Administration (FDA)
approved  treatments  available.  In order to meet this threat,  SIGA scientists
have  identified  a  lead  drug  candidate,  SIGA-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 arenavirus  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
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,  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.


                                       1


      Surface Protein  Expression  (SPEX) System:  Our scientists have harnessed
the protein expression  pathways of gram-positive  bacteria and turned them into
protein production factories.  Using our proprietary SPEX system, we can produce
foreign  proteins at high levels in the  laboratory  for use in subunit  vaccine
formulations.  Furthermore,  we  can  envision  engineering  these  bacteria  to
colonize  the  mucosal   surfaces  of  soldiers  and/or  civilians  and  secrete
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 hit 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 U.S.  government's  proposed  budget for the  Department  of  Homeland
Security (the "DHS") for the fiscal year beginning October 1, 2005 includes $2.5
billion of federal  spending on Project  BioShield.  In addition to contributing
funds to the DHS,  the  Department  of Defense  will be looking  for  innovative
approaches to the prevention and treatment of biological  warfare agents. One of
the major concerns is Smallpox -- although declared extinct in 1980 by the World
Health Organization,  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 Centers
for Disease  Control and  Prevention  (the  "Centers  for Disease  Control")  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.  At an estimated $15 per dose,  the cost
would be approximately  $900 million.  Further the CBO reports that the DHS will
spend an additional $1 billion to replace expired stocks in 2007-2013.

      The FDA has 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  potential  products  in animal  models
approved  for sale  within a  relatively  short time frame if our  programs  are
successful.  Our  Chief  Scientific  Officer,  Dennis  Hruby,  has over 20 years
experience  working  on  Smallpox-related   research  and  has  been  leading  a
SIGA/Oregon State University consortium working on an antiviral drug development
project for the past two years.

      The market  potential 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  government's  purchase of  approximately  $800
million worth of an older version  Smallpox vaccine to have an inventory on hand
if needed is evidence of such market potential.

                     SIGA Anti-Infectives Product Portfolio

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


                                       2


to its target tissue.  We believe that, by preventing  attachment,  the bacteria
should be readily cleared by the body's immune system.

      Gram-Positive  Antibiotic  Technology:   One  of  our  key  anti-infective
programs is based on a novel target for antibiotic therapy.  Our scientists have
identified an enzyme, a selective protease,  used by most Gram-positive bacteria
to anchor certain  proteins to the bacterial cell wall.  These surface  proteins
are the  means by which  certain  bacteria  recognize,  adhere  to and  colonize
specific  tissue.  Our  strategy  is to  develop  protease  inhibitors  as novel
antibiotics.  We believe  protease  inhibitors will have wide  applicability  to
Gram-positive bacteria in general, including antibiotic resistant staphylococcus
and a broad  range of  serious  infectious  diseases  including  meningitis  and
respiratory tract infections.  In 1997, we entered into a collaborative research
and license agreement with Wyeth to identify and develop protease  inhibitors as
novel antibiotics. In the first quarter of 2001, we received a milestone payment
from Wyeth for delivery of the first  quantities of protease for screening,  and
high-throughput  screening for protease inhibitors was initiated.  In connection
with our effort on this program we have entered  into a license  agreement  with
the University of California at Los Angeles for certain  technology  that may be
incorporated  into our  development  of  products  for  Wyeth.  High  throughput
screening  of compound  libraries  has been  completed  and lead  compounds  are
currently being evaluated in the laboratory and in animals.

      Gram-Negative  Antibiotic  Technology:  In 1998,  we entered into a set of
technology  transfer and related  agreements with MedImmune,  Inc., Astra AB and
Washington  University,   pursuant  to  which  we  acquired  rights  to  certain
Gram-negative  antibiotic targets,  products,  screens and services developed at
Washington University. In February 2000, we ended our collaborative research and
development  relationship  with Washington  University on this technology.  (See
"Collaborative  Research and Licenses").  We maintain a non-exclusive license to
technology  acquired  through  these  related  agreements.  We  are  using  this
technology in the development of antibiotics against Gram-negative pathogens. As
described above,  these bacteria use structures  called pili to adhere to target
tissue,  and we plan to  exploit  the  assembly  and  export of these  essential
infective  structures as novel  anti-infective  targets.  We continue to work on
enhancing  the  intellectual  property  that we jointly  share  with  Washington
University.

      Broad-Spectrum Antibiotic Technology: An initial host response to pathogen
invasion  is the  release  of oxygen  radicals,  such as  superoxide  anions and
hydrogen peroxide. The DegP protease is a first-line defense against these toxic
compounds,  which  are  lethal  to  invading  pathogens,  and is a  demonstrated
virulence  factor for  several  important  Gram-negative  pathogens:  Salmonella
typhimurium,  Salmonella typhi, Brucella melitensis and Yersinia enterocolitica.
In all  of  these  pathogens  it  was  demonstrated  that  organisms  lacking  a
functional DegP protease were  compromised for virulence and showed an increased
sensitivity  to oxidative  stress.  It was also  recently  demonstrated  that in
Pseudomonas  aeruginosa  conversion  to  mucoidy,  the  so-called  CF  phenotype
involves two DegP homologues.

      Our scientists  recently  demonstrated that the DegP protease is conserved
in Gram-positive pathogens,  including S. pyogenes, S. pneumoniae, S. mutans and
S. aureus.  Moreover, our investigators have shown a conservation of function of
this  important  protease in  Gram-positive  pathogens  and we believe that DegP
represents a true broad-spectrum anti-infective development target. Our research
has  uncovered a  virulence-associated  target of the DegP protease that will be
used to design an assay for high-throughput  screening for the identification of
lead inhibitors of this potentially important anti-infective target.

                       Market for Anti-infective Programs.

      There  are  currently  more than 100  million  prescriptions  written  for
antibiotics  annually  in the U.S.  and we  estimate  the  worldwide  market for
antibiotics to be more than $26 billion.  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.


                                       3


                                   Technology

      Anti-Infectives Technology: Prevention of Attachment and Infectivity

      The  bacterial   infectious   process  generally   includes  three  steps:
colonization,  invasion  and  disease.  The  adherence  of  bacteria to a host's
surface is crucial  to  establishing  colonization.  Bacteria  adhere  through a
number  of  mechanisms,  but  generally  by  using  highly  specialized  surface
structures  which,  in turn,  bind to specific  structures  or  molecules on the
host's cells or, as discussed below, to inanimate  objects residing in the host.
Once adhered,  many  bacteria will invade the host's cells and either  establish
residence or continue invasion into deeper tissues.  During any of these stages,
the invading bacteria can cause the outward  manifestations of disease,  in some
cases through the  production  and release of toxin  molecules.  The severity of
disease,  while dependent on a large combination of factors, is often the result
of the ability of the bacteria to persist in the host. These bacteria accomplish
this  persistence  by  using  surface  molecules  which  can  alter  the  host's
nonspecific  mechanisms  or its highly  specific  immune  responses  to clear or
destroy the organisms.

      Unlike conventional  antibiotics,  our  anti-infectives  approaches aim to
block the ability of pathogenic bacteria to attach to and colonize human tissue,
thereby preventing  infection at its earliest stage. Our scientific  strategy is
to inhibit the expression of bacterial  surface proteins  required for bacterial
infectivity.  We  believe  that  this  approach  has  promise  in the  areas  of
hospital-acquired  drug-resistant infections and a broad range of other diseases
caused by bacteria.

      Many  special  surface  proteins  used by  bacteria to infect the host are
anchored in the bacterial cell wall.  Scientists at The  Rockefeller  University
("Rockefeller")  have  identified an amino acid sequence and related  enzyme,  a
selective protease,  that are essential for anchoring proteins to the surface of
most Gram-positive  bacteria.  Published  information  indicates that this amino
acid sequence is shared by more than 50 different  surface  proteins  found on a
variety of Gram-positive  bacteria. This commonality suggests that this protease
represents a promising  target for the  development of a new class of antibiotic
products for the treatment of a wide range of infectious  diseases.  Experiments
by our scientists have shown that without this sequence,  proteins cannot become
anchored to the bacterial surface and thus the bacteria are no longer capable of
attachment,  colonization  or  infection.  Such  "disarmed"  bacteria  should be
readily cleared by the body's immune system.  Our drug discovery  strategy is to
use a combination of structure-based  drug design and high throughput  screening
procedures to identify compounds that inhibit the protease, thereby blocking the
anchoring process. If successful,  this strategy should provide relief from many
Gram-positive  bacterial  infections,  but may prove  particularly  important in
combating  diseases  caused  by  the  emerging  antibiotic   resistance  of  the
Gram-positive organisms Streptococcu,  aureus, Streptococcus pneumoniae, and the
enterococci.

      In contrast to the above program, which focuses on Gram-positive bacteria,
our pilicide  program,  based upon  initial  research  performed  at  Washington
University in St. Louis  ("Washington  University"),  focuses on a number of new
and novel targets all of which impact on the ability of  Gram-negative  bacteria
to assemble  adhesive pili on their surfaces.  Pili are proteins on the surfaces
of Gram-negative bacteria -- such as E. coli,  salmonella,  and shigella -- that
are required for the attachment of the bacteria to human tissue,  the first step
in  the   infection   process.   This   research   program  is  based  upon  the
well-characterized  interaction  between a periplasmic protein -- a chaperone --
and the protein  subunits  required to form pili. In addition to describing  the
process by which  chaperones  and pili subunits  interact,  we have developed an
assay systems necessary to screen for potential therapeutic compounds,  and have
provided  an  initial  basis  for  selecting  novel  antibiotics  that  work  by
interfering with the pili adhesion mechanism.

           Vaccine Technologies: Mucosal Immunity and Vaccine Delivery

      Using proprietary technology licensed from 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


                                       4


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  Streptococcus  gordonii ("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 World Health Organization (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 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


                                       5


            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.

      Strep Throat Vaccine Candidate.  Until the age of 15, many children suffer
from recurrent  strep throat  infections.  Up to three percent of  ineffectively
treated strep throat cases progress to rheumatic  fever,  a  debilitating  heart
disease, which worsens with each succeeding streptococcal  infection.  Since the
advent  of  penicillin  therapy,  rheumatic  fever  in  the  United  States  has
experienced  a dramatic  decline.  However,  in the last two decades,  rheumatic
fever has experienced a resurgence in the United States.  Part of the reason for
this is the latent  presence of this  organism  in  children  who do not display
symptoms of a sore throat,  and,  therefore,  remain  untreated  and at risk for
development  of  rheumatic  fever.  Based on data from the  Centers  for Disease
Control and Prevention, there are five to 10 million cases of pharyngitis due to
group A streptococcus  in the United States each year. There are over 32 million
children in the principal age group targeted by us for  vaccination.  Worldwide,
it is estimated  that one percent of all school age  children in the  developing
world have rheumatic heart disease.  Additionally,  despite the relative ease of
treating strep throat with antibiotics,  the specter of antibiotic resistance is
always present. In fact, resistance to erythromycin,  the second line antibiotic
in patients allergic to penicillin, has appeared in a number of cases.

      o     We  believe  that the reason no  vaccine  for strep  throat has been
            developed  is because of problems  associated  with  identifying  an
            antigen that is common to the more than 120  different  serotypes of
            group A  streptococcus,  the bacterium  that causes the disease.  We
            have licensed from Rockefeller a proprietary antigen which is common
            to most types of group A  streptococcus,  including  types that have
            been associated with rheumatic  fever.  When this antigen was orally
            administered to animals,  it was shown to provide protection against
            multiple  types  of  group A  streptococcal  infection.  Using  this
            antigen,  we are  seeking  to  develop a mucosal  vaccine  for strep
            throat.

      o     SIGA  has  taken a  parallel  vaccine  development  track  with  two
            formulations  of the  cross-protective  streptococcal  antigen.  One
            approach  expresses  the strep throat  antigen on the surface of the
            commensal  bacterium,  Streptococcus  gordonii,  which  lives on the
            surface  of the teeth and gums.  Pre-clinical  research  in mice and
            rabbits has  established  the ability of this  vaccine  candidate to
            colonize and induce both a local and systemic immune  response.  The
            other candidate uses a subunit (purified protein) approach, in which
            the  antigen  is  delivered  intranasally  with a  mucosal  adjuvant
            (enhances the immune  response).  Like the commensal  approach,  the
            subunit  approach has provided  significant  protection in mice from
            challenges  by multiple  serotypes.  We are  collaborating  with the
            National Institutes of Health ("NIH") and the University of Maryland
            Center for Vaccine  Development on the clinical  development of this
            vaccine  candidate.   In  cooperation  with  the  NIH  we  filed  an
            Investigational  New  Drug  Application  ("IND")  with  the  FDA  in
            December 1997. The first stage of these clinical  trials,  using the
            commensal  delivery  system without the strep throat  antigen,  were
            completed at the  University  of Maryland in 2000.  The study showed
            the  commensal  delivery  system  to be  well-tolerated  and that it
            spontaneously  eradicated or was easily  eradicated by  conventional
            antibiotics.  A  second  clinical  trial of the  commensal  delivery
            system without the strep throat antigen was initiated in 2000 at the
            University of Maryland.  The study was completed in January 2002 and
            the results  corroborated the results of the earlier study regarding
            tolerance and spontaneous eradication. Further development continues
            principally  on  the  subunit   approach,   which  is  currently  in
            pre-clinical studies.

      o     In the U.S.  there are about 19 million  children  aged 2 to 6 years
            who could be candidates to receive such a vaccine at the time of its
            introduction  and then around 4 million  babies born each year to be
            protected.  Assuming a charge of $25 per dose and three doses needed
            for protection, there could be a potential market for a strep throat
            vaccine of $1.4 billion to


                                       6


            immunize  the  entire  U.S.  population  of 2 to 6  year  olds  and,
            thereafter,  $300 million per year to maintain  immunization  in new
            births.

                   Surface Protein Expression System ("SPEX")

      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 E. coli has been the  method of choice to  express a variety  of
gene   products,   because   of  these   bacteria'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  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.


                                       7


                                  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  $9.4  million,  $5.3 million and
$3.3 million for the years ended December 31, 2004, 2003 and 2002, respectively.
As  of  December  31,  2004,  2003  and  2002,  our   accumulated   deficit  was
approximately $44.2 million, $34.8 million and $29.5 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  and financial  condition 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  through  September 30, 2006.  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;


                                       8


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 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.  Our biological warfare defense products do not need human clinical
trials for  approval by the FDA.  We will need to perform two animal  models and
provide  safety data for a product to be approved.  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:

o     be safe, non-toxic and effective;

o     otherwise meet applicable regulatory standards;

o     receive the necessary regulatory approvals;

o     develop into commercially viable drugs;

o     be manufactured or produced economically and on a large scale;

o     be successfully marketed;

o     be reimbursed by government and private insurers; and

o     achieve customer acceptance.


                                       9


      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 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  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, 2004,  2003 and 2002,  respectively,  were derived from
revenues related to grants,  contracts and license  agreements.  We will receive
little or no revenues under our collaborative  agreements if our  collaborators'
research,   development  or  marketing  efforts  are  unsuccessful,  or  if  our
agreements  are  terminated  early.  Additionally,  if we do not enter  into new
collaborative  agreements, we will not receive future revenues from new sources.
Our future  revenue  is  substantially  dependent  on the  continuing  grant and
contract work being performed for the NIH under two major grants which expire in
September  2006,  the U.S. Army which expires at the end of December 2007, and a
new contract  with the U.S.  Army which is funded  through the United States Air
Force and expires in October 2006.  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.

      Several   factors  will  affect  our  future   receipt  of  revenues  from
collaborative arrangements,  including the amount of time and effort expended by
our  collaborators,  the timing of the identification of useful drug targets and
the  timing of the  discovery  and  development  of drug  candidates.  Under our
existing  agreements,  we may not earn significant  milestone payments 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  $12.1 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 Air Force (USAF). In September, 2005, we entered into a $3.2
      million,  one year contract  with the United States Army Medical  Research
      and  Material   Command   ("USAMRMC").   The  agreement,   for  the  rapid
      identification and treatment of anti-viral diseases, is funded through the
      USAF.  Advance  payments  under  the  agreement,  received  prior  to  the
      performance  of services,  are deferred and  recognized  as revenue as the
      related  services are  performed.  In October,  2005, we received  advance
      payment of $1.0  million.  Three equal  advance  payments of $733,333  are
      scheduled for on or about January 1, 2006, April 1, 2006 and July 1, 2006.

o     U.S. Army Medical  Research  Acquisition  Activity.  In December  2002, we
      entered into a four years  contract  with the U.S.  Army Medical  Research
      Acquisition Activity (USAMRAA) to develop a drug to treat Smallpox. We are
      current in all our obligations under our agreement.

o     In  September,  2005,  we  entered  into an  agreement  with  Saint  Louis
      University for the continued  development of one of the Company's  leading
      compounds.  The agreement is funded  through the NIH. Under the agreement,
      we 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.


                                       10


o     The 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.

o     Oregon State University ("OSU").  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     Wyeth.  Our license  agreement  expires on the earlier of June 30, 2007 or
      the last to expire patent that we have sub-licensed to them. Wyeth has the
      right to terminate the agreement on 90 days written notice. If terminated,
      all rights  granted to Wyeth will  revert to us,  except for any  compound
      identified  by Wyeth prior to the date of  termination  and subject to the
      milestones and royalty obligations of the agreement.

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.  This agreement is
      related to our  agreement  with Wyeth and expires at the same time as that
      agreement. It can be cancelled earlier if we default on our obligations or
      if Wyeth  cancels  its  agreement  with SIGA and we are not able to find a
      replacement  for Wyeth.  We have currently met all our  obligations  under
      this agreement.

o     TransTech Pharma,  Inc. Under our  collaborative  agreement with TransTech
      Pharma,  TransTech  Pharma  is  required  to  collaborate  with  us on the
      discovery,  optimization  and development of lead compounds to 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


                                       11


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.

      Before  commencing  clinical trials in humans,  we must submit and receive
clearance  from  the  FDA  by  means  of an  Investigational  New  Drug  ("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.


                                       12


      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 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 growth has placed,  and may continue to place, a
significant strain on our management and operations.


                                       13


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  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


                                       14


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,  if any,
after they are 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;

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 genetically  engineered  commensals is 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.

      Although our  management  believes  that we have the ability to acquire or
produce quantities of genetically  engineered  commensals  sufficient to support
our present needs for research and our projected needs for our initial  clinical
development programs, management believes that improvements in our manufacturing
technology  will  be  required  to  enable  us  to  meet  the  volume  and  cost
requirements  needed for certain commercial  applications of commensal products.
Products based on commensals have never been manufactured on a commercial scale.
The  manufacture  of all  of  our  products  will  be  subject  to  current  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


                                       15


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, 2004,  Directors,  Officers  and  principal  stockholders
beneficially owned approximately 48.1% of our stock.

                              ABOUT THIS PROSPECTUS

      This prospectus is part of a registration statement that we filed with the
Securities and Exchange  Commission.  The prospectus relates to 2,000,000 shares
of our common stock which the selling  stockholders named in this prospectus may
sell from time to time and  1,060,000  shares of our common  stock  which may be
issued under certain warrant 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,


                                       16


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, 2004,  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.

                                 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.


                                       17


                              SELLING STOCKHOLDERS

      The table below sets forth information  regarding  ownership of our common
stock by the selling  stockholders  as of November 15,  2005,  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 November 15, 2005. As of November
15, 2005, 26,500,648 shares of our common stock were outstanding.



                                       Securities Owned Prior to Offering             Securities Owned After Offering (1)
                                                                  Shares of Common
                                  Shares of       Percent of       Stock Offered      Number of Shares        Percent of
Name of Selling Stockholder      Common Stock    Common Stock          Hereby         of Common Stock        Common Stock
                                                                                                      
Smithfield Fiduciary LLC               750,000          2.83%             750,000                 --                 0.0%
Omicron Master Trust                   750,000          2.83%             750,000                 --                 0.0%
Iroquois Capital LP                    750,000          2.83%             750,000                 --                 0.0%
Cranshire Capital LP                   750,000          2.83%             750,000                 --                 0.0%
Gary J. Shemano                        110,000          0.42%              22,000                 --                 0.0%
Michael R. Jacks                        31,500          0.12%              16,500                 --                 0.0%
William Corbett                        103,500          0.39%              16,500                 --                 0.0%
Terrence Cush                            5,000          0.02%               5,000                 --                 0.0%


      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.


                                       18


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.

      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.


                                       19


      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.

                                  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, 2004 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.


                                       20


                             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.

                           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, 2004;

      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;

      o     quarterly report on Form 10-Q for the quarter ended March 31, 2005;

      o     quarterly report on Form 10-Q for the quarter ended June 30, 2005;

      o     quarterly  report on Form 10-Q for the quarter  ended  September 30,
            2005; and

      o     our current  reports on Form 8-K filed on February 15,  2005,  April
            26, 2005,  May 3, 2005,  May 27, 2005,  August 11, 2005,  August 24,
            2005,  September 20, 2005,  September 27, 2005,  September 28, 2005,
            October 6, 2005, and November 4, 2005.

      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.


                                       21