As filed with the Securities and Exchange Commission on April 14, 2003



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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                              ---------------------
                                    FORM S-3
                             REGISTRATION STATEMENT
                        UNDER THE SECURITIES ACT OF 1933
                             ----------------------

                               APHTON CORPORATION
             (Exact name of registrant as specified in its charter)

   Delaware                                                     95-3640931
(State or other            80 S.W. Eighth Street              (I.R.S. Employer
jurisdiction of                 Suite 2160                Identification Number)
incorporation or            Miami, Florida 33130
organization                  (305) 374-7338

                        (Address, including zip code, and
                    telephone number, including area code, of
                    registrant's principal executive offices)
                           ---------------------------

                                 Philip C. Gevas
                 Chairman, President and Chief Executive Officer
                               Aphton Corporation
                        80 S.W. Eighth Street, Suite 2160
                              Miami, Florida 33130
                                 (305) 374-7338
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

                                   Copies to:

                             Jonathan E. Kahn, Esq.
                                White & Case LLP
                          1155 Avenue of the Americas
                            New York, New York 10036

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

     Approximate date of commencement of proposed sale to the public:  From time
to time after this Registration Statement becomes effective.

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

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

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

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

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

<TABLE>
<CAPTION>
                                           CALCULATION OF REGISTRATION FEE

============================================================================================================
                                                     PROPOSED MAXIMUM    PROPOSED MAXIMUM       AMOUNT OF
         TITLE OF SECURITIES         AMOUNT TO       AGGREGATE PRICE     AGGREGATE OFFERING    REGISTRATION
          TO BE REGISTERED         BE REGISTERED       PER SHARE(2)            PRICE               FEE
------------------------------------------------------------------------------------------------------------
<S>                                   <C>                  <C>                 <C>               <C>
Common Stock, $.001 par value(1)      150,000              $2.58               $387,000          $31.31
============================================================================================================
</TABLE>

(1)  Issuable upon the exercise of the warrants.
(2)  Estimated   solely  for  the  purpose  of  computing   the  amount  of  the
     registration fee in accordance with Rule 457 of the Securities Act of 1933,
     as amended, based on the average high and low prices reported on the Nasdaq
     National Market on April 11, 2003.

     We hereby amend this Registration Statement on such date or dates as may be
necessary to delay its effective  date until we file a further  amendment  which
specifically  states that this  Registration  Statement shall thereafter  become
effective in  accordance  with Section 8(a) of the  Securities  Act of 1933,  as
amended or until the Registration  Statement shall become effective on such date
as the  Commission,  acting  pursuant  to  said  Section  8(a),  may  determine.
================================================================================
<PAGE>

THE INFORMATION IN THIS 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 PROSPECTUS IS NOT AN OFFER
TO SELL THESE SECURITIES AND IT IS NOT SOLICITING AN OFFER TO BUY THESE
SECURITIES IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED.

                  SUBJECT TO COMPLETION, DATED APRIL 14, 2003

                                   PROSPECTUS

                               APHTON CORPORATION

            150,000 Shares of Common Stock, Par Value $.001 per Share
               --------------------------------------------------

     The selling  stockholder  named on page 15 of this prospectus may offer for
sale up to 150,000 shares of our common stock which may be issued as a result of
the  exercise  of the  warrants  held by the  selling  stockholder.  We will not
receive any of the proceeds from the sale of the shares of our common stock.

     We have been advised by the selling stockholder that it may or may not sell
all or a portion of the shares of our common  stock from time to time on Nasdaq.
It may also make private  sales of the shares of our common stock to  purchasers
directly. Alternatively, it may from time to time offer the shares of our common
stock  through  underwriters,  brokers,  dealers  or  agents,  who  may  receive
compensation in the form of underwriting discounts, commissions or concessions.

     Our common stock is listed on the Nasdaq  National  Market under the symbol
"APHT." On April 11,  2003,  the last  reported sale price of our common stock
reported on Nasdaq was $2.58.

     Investing in our common stock involves risks. See "Risk Factors"  beginning
on page 4 of this  prospectus  for a  discussion  of certain  factors you should
consider before you buy our common stock.

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

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

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

                 The date of this prospectus is April 14, 2003
<PAGE>

                                TABLE OF CONTENTS

ABOUT THIS PROSPECTUS..........................................................1

THE COMPANY....................................................................1

RISK FACTORS...................................................................4

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

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

THE SELLING STOCKHOLDER.......................................................15

PLAN OF DISTRIBUTION..........................................................16

LEGAL MATTERS.................................................................17

EXPERTS.......................................................................18

WHERE YOU CAN FIND MORE INFORMATION...........................................18

INCORPORATION OF DOCUMENTS BY REFERENCE.......................................18

                    --------------------------------
<PAGE>

                              ABOUT THIS PROSPECTUS

     This  prospectus  is part of a  registration  statement on Form S-3 that we
filed with the Securities and Exchange  Commission using a "shelf"  registration
process.  Under this process,  the selling  stockholder  may, from time to time,
sell up to 150,000  shares of our common  stock in one or more  offerings.  This
prospectus does not contain all of the information  included in the registration
statement and the exhibits thereto. Statements included in this prospectus as to
the  contents of any contract or other  document  that is filed as an exhibit to
the registration  statement are not necessarily complete and you should refer to
that  agreement or document for a complete  description  of these  matters.  You
should read both this  prospectus and any prospectus  supplement,  together with
the additional information described in this prospectus under the heading "Where
You Can Find More Information."

                                   THE COMPANY

     Aphton Corporation ("we," "Aphton" or the "Company") is a biopharmaceutical
company.  We are engaged in research and development and conduct clinical trials
for our products,  both independently and with our corporate strategic partners.
We apply our  innovative  active  immunization  technology-platform  to  develop
products for  neutralizing,  and removing from  circulation,  hormones and other
molecules that participate in  gastrointestinal  system and reproductive  system
cancer and non-cancer  diseases.  We also are developing a product to neutralize
hormones to prevent pregnancy.

     Since 1997 we have had a strategic alliance with Pasteur Merieux Connaught,
now Aventis Pasteur, for products that treat gastrointestinal  cancers, in North
America and Europe. Since 1998, we have had a strategic alliance with SmithKline
Beecham,  now  GlaxoSmithKline,  for  products  that treat  reproductive  system
cancers and non-cancer diseases, worldwide.

     During our first  five  years,  we  developed  the basis of our  innovative
active immunization  (vaccine) technology and our monoclonal antibody technology
and have  continued  developing  them to date.  In our  second  five  years,  we
initiated the development of products based on those technology platforms, which
we have  continued  to date.  Since our  inception,  we have  developed a patent
estate to protect  our  technology  platforms  and our  products  after they are
commercialized.  During this period and since,  together with our  collaborating
scientists,  we have  developed the  scientific  foundations  and the scientific
literature  relating to the central role of gastrin and gastrin receptors in the
onset, development, growth and spread of adenocarcinomas of the gastrointestinal
system from the  esophagus  to the  stomach,  pancreas and liver and through the
colon and rectum.

     After conducting toxicology testings and pre-clinical trials in animals, we
initiated  phase I safety  and  phase II  dose-ranging/indications  of  efficacy
clinical trials, with G17DT and GnRH pharmaccine.  These trials demonstrated for
the first  time that a  patient's  immune  system  can be  activated  to target,
neutralize and inhibit  hormonal growth factors that fuel cancers and drive them
to  metastasize  (spread).  We  recently  reported  successful  results  from  a
randomized, double-blind, phase III trial with G17DT as monotherapy for advanced
pancreatic  cancer and from a phase II gastric (stomach) cancer trial with G17DT
in combination with the chemotherapeutics

                                      -1-
<PAGE>

cisplatin  and 5-FU.

     We achieved our  developments,  pre-clinical  and clinical results with the
expenditure of approximately  $134 million in the twelve years since our initial
public  offering in 1991. We believe we can reduce our spending  during the next
twelve  months by more than 60% to less than $16 million from the  approximately
$40 million  during the twelve  months of fiscal  year 2002.  We will pursue our
primary  objective of filing for approval to market  G17DT for  monotherapy  for
advanced  pancreatic cancer patients in the European Union, Canada and Australia
by September 2003. We currently have a strategic  alliance with Aventis Pasteur,
whereby Aventis will exclusively promote, advertise, market, distribute and sell
our  anti-gastrin  vaccine  (G17DT) in North  America and  Europe.  We intend to
license  G17DT to  third  parties  to  treat  human  cancers  in  other  markets
worldwide,  including Japan. We also intend to license  worldwide our monoclonal
antibody  products to target  gastrointestinal  system  cancers.  For non-cancer
therapies,  we intend to license  G17DT for the  treatment  of  gastroesophageal
reflux disease (GERD).

Clinical Trials

     We are currently  completing  the following  clinical  trials:  a phase III
trial  conducted  outside of the United  States for  pancreatic  cancer with its
anti-gastrin  17 immunogen  (G17DT) as a monotherapy;  a phase II clinical trial
conducted in the United States and foreign countries,  with G17DT in combination
with the chemotherapeutics cisplatin and 5-FU for gastric cancer patients; and a
phase II trial in Europe with GnRH pharmaccine for prostate cancer patients.  We
are  conducting  a second  phase  III  trial  that has  also  completed  patient
recruitment, conducted in the United States and foreign countries for pancreatic
cancer with G17DT in combination with the chemotherapeutic  gemcitabine. We have
initiated but are not currently  recruiting patients pending funding for a phase
II trial in Europe with G17DT for  gastroesophageal  reflux disease  (GERD),  or
"severe  heart burn"  patients.  In addition,  our Phase II clinical  trial with
respect to  immuno-contraception  has been  initiated  but is "on hold"  pending
further funding from the World Health Organization (WHO).

     We believe  that the results of the  randomized,  double  blind,  phase III
trial  conducted in foreign  countries with G17DT as a monotherapy  for advanced
pancreatic  cancer  patients  are already  sufficient  for filing for  marketing
approval in the European Union, Canada and Australia.  Therefore,  we have begun
the process of  gathering  and  compiling  the data and the  preparation  of the
extensive  regulatory   documentation  required  for  submission  for  marketing
approval.  This process can be expected to take  approximately  five months, but
that cannot be stated with  certainty.  We expect that we will receive  priority
review  of the  filings.  The time for  review  and the  granting  of  marketing
approval  in  each  jurisdiction  cannot,  however,  be  predicted  by  us  with
certainty.

     In addition,  we believe that the results of our phase II trial for gastric
cancer patients treated with G17DT in combination with cisplatin and 5-FU can be
described as "impressive." We plan to investigate the possibility of obtaining a
conditional  marketing approval for this therapy in a foreign jurisdiction based
on these results, when the final data is compiled, analyzed and documented.

                                      -2-
<PAGE>

Financial Strategy

     We  finance  our  operations  through  the sale of our  equity  securities,
convertible  debentures  and  licensing  fees.  These funds  provide us with the
resources  to  operate  our  business,  attract  and retain  key  personnel  and
scientific  staff,  fund our  research  and  development  program,  pre-clinical
testing and clinical  trials,  obtain the  necessary  regulatory  approvals  and
develop our technology and products.

     We anticipate that our existing capital resources,  which consist primarily
of cash and  short-term  cash  investments,  including (1) the proceeds from the
sale of convertible, redeemable, 5-year, interest-bearing notes and unregistered
warrants to three institutional investors, including a substantial participation
by two existing  investors in Aphton,  sold in two tranches,  of which the first
$15 million tranche closed on March 31, 2003 and the second $5 million  tranche,
the closing of which is subject to the  fulfillment of certain  conditions;  (2)
the  gross  proceeds  of $1.48  million  from the  sale of our  common  stock on
February  24, 2003 and gross  proceeds of $18,750  from the  concurrent  sale of
unregistered  warrants  to an  institutional  investor;  and (3)  proceeds of $3
million  from the issuance on December  19, 2002 of a  convertible,  redeemable,
5-year,  interest  bearing  note to Aventis  Pharmaceuticals,  Inc. and interest
thereon, will enable us to maintain a range of operations into the first quarter
of 2004.  Our  working  capital  and  capital  requirements  depend on  numerous
factors, including the following:

     o    the  progress of our  research and  development  program,  preclinical
          testing and clinical trials;

     o    the timing and cost of obtaining regulatory approvals;

     o    the  levels  of  resources  that we  devote  to  product  development,
          manufacturing and marketing capabilities;

     o    technological advances;

     o    competition; and

     o    collaborative  arrangements  or  strategic  alliances  with other drug
          companies,  including  the  further  development,   manufacturing  and
          marketing  of certain of our  products and our ability to obtain funds
          from such strategic alliances or from other sources.

     Many of these factors are beyond our control.  In the event that we require
additional  funds,  we may be required to sell  additional  securities,  whether
equity, convertible debt or otherwise. In addition, we may be required to obtain
funds through  arrangements with  collaborative  partners that may require us to
negotiate  agreements  which may be less than favorable to us, if we are able to
secure them at all. If we are unable to complete  such  transactions,  we may be
required to delay, reduce the scope of, or eliminate one or more of our research
or development programs.

                                      -3-
<PAGE>

                                  RISK FACTORS

     If you purchase  shares of our common  stock,  you will take on a financial
risk. In deciding whether to invest, you should consider carefully the following
factors, the information  contained in this prospectus and the other information
to which we have referred you.  Additional risks and uncertainties not presently
known to us or that we currently do not  consider  material  also may impair our
business operations. If any of the following risks actually occur, our business,
financial  condition  or results of  operations  could be  materially  adversely
affected. In such case, the trading price of our common stock could decline, and
you may lose all or part of your investment.

     Our potential products are in various stages of product  development.  Some
of our potential products are in research or in early  development,  and we have
generated no revenues from product sales. Our most advanced  potential  product,
an immunogen to treat pancreatic  cancer,  is in a phase III trial in the United
States  and  Europe.  Our other  potential  products  to treat  stomach  cancer,
colorectal  cancer,  gastroesophageal  reflux disease (or GERD),  chronic peptic
ulcers, breast cancer,  endometriosis and prostate cancer are mostly at phase II
but some potential  products are in even earlier phases of  development.  All of
our potential  products will require  expensive and  extensive,  time  consuming
clinical  testing,  and some may require  additional  research and  development,
prior to commercial use.  Accordingly,  we cannot plan on deriving revenues from
these products for a number of years,  if at all. These  potential  products may
not be developed successfully into immunogens that can be administered to humans
or may not prove to be safe and effective in clinical  trials or  cost-effective
to manufacture and administer. We may encounter problems in clinical trials that
will cause us to delay or suspend a clinical trial.  Also, our products that are
currently  under  development  may not be  completed  successfully  or within an
acceptable  time  period,  if at all.  Further,  our  products  may not  receive
regulatory  approval.  Finally,  if any  of our  products  do  receive  required
regulatory  approval,  we may not be  capable of  producing  those  products  in
commercial quantities or those products may not be accepted by the marketplace.

     We expect to continue  incurring  substantial  operating losses in the next
several  years.  We have  experienced  significant  operating  losses  since our
inception in 1981 and expect to continue incurring  substantial operating losses
for at least the next several years. We expect losses to increase as a result of
the expenses  associated with clinical testing and research and development.  As
of December 31, 2003,  we had an  accumulated  deficit of  approximately  $140.6
million. Our ability to achieve profitability depends upon our ability, alone or
through relationships with third parties, to develop successfully our technology
and products, to obtain required regulatory approvals and to manufacture, market
and sell such products.

     We have never paid any  dividends  and do not expect to pay cash  dividends
before significant product revenues, if any, are realized, if then. In addition,
there is a provision in the senior convertible notes we issued on March 31, 2003
that,  for so long as such notes are  outstanding,  restricts us from paying any
cash  dividend or  distribution  on our common stock  without the prior  express
written  consent  of the  holders  of such  notes  representing  not  less  than
two-thirds of the aggregate principal amount of the then outstanding notes.

                                      -4-
<PAGE>

     We have substantial  capital  requirements and we may not be able to obtain
additional  financing.  Developing  our  technology  and products will require a
commitment  of  substantial  funds to  conduct  the  costly  and  time-consuming
research and clinical trials necessary for such development.  Our future capital
requirements will depend on many other factors, including:

     o    continued   scientific   progress  in  the  research  and  development
          (clinical trials) of our products;

     o    our ability to collaborate with others for the manufacture,  marketing
          and sale of our products;

     o    the cost of regulatory approvals;

     o    the  cost of  establishing,  maintaining  and  enforcing  intellectual
          property rights;

     o    competing technological and market developments; and

     o    changes in our existing research relationships.

     Although we intend to reduce our spending  during the next twelve months by
more than 60% to less than $16 million from the  approximately $40 million spent
during  the 12 months of  fiscal  year  2002,  it is  possible  that our rate of
expenditure may further increase if we pursue  pre-clinical  studies or clinical
trials for our other products at a faster rate than we currently anticipate.  We
believe that our current capital resources,  which consist primarily of cash and
cash equivalents,  should be sufficient,  barring unforeseen  circumstances,  to
fund our operating  expenses and capital  requirements as currently planned into
the first quarter of the year 2004.

     We may seek  additional  financing  through  collaborative  arrangements or
through public or private equity or debt  financings.  Additional  financing may
not be available  to us on  acceptable  terms or at all. If we raise  additional
funds by issuing  equity  securities,  dilution  to the  interests  of  existing
stockholders may result. If adequate funds are not available, we may be required
to  delay,  reduce  the scope of or  eliminate  one or more of our  research  or
development  programs or obtain funds through  arrangements  with  collaborative
partners or others that may  require us to  relinquish  rights to certain of our
technologies,  potential  products or products that we would  otherwise  seek to
develop or commercialize ourselves.

     Our different  approach to disease treatment may not prove successful.  Our
products  under  development  are based on an  approach  to disease  therapy and
prevention which has not yet been approved. Our approach may ultimately prove to
be unsuccessful since:

     o    we may not successfully complete our product development efforts;

     o    our products may not be proven to be safe and effective;

     o    we may not receive approval from the U.S. Food and Drug Administration
          or FDA, or any other applicable regulatory agencies; or

                                      -5-
<PAGE>

     o    medical centers, hospitals,  physicians or patients may not accept our
          products  as readily  as  current  drug  therapies  or other  forms of
          treatment.

     Undesirable and unintended side effects or unfavorable publicity concerning
any of our products or other  products  incorporating  a similar  approach could
limit or curtail commercial use of our products and could have an adverse effect
on our  ability to obtain  regulatory  approvals  and to achieve  physician  and
patient acceptance.

     The  development  of our products is subject to extensive  regulation.  The
research, pre-clinical development, clinical trials, manufacturing and marketing
of our  products are subject to extensive  regulation  by numerous  governmental
authorities  in the  United  States  and other  countries.  Clinical  trials and
manufacturing  and marketing of products  undergo  rigorous testing and approval
processes by the FDA and equivalent  foreign regulatory  authorities,  including
the Medicines  Control  Agency,  or MCA, in the United  Kingdom.  The process of
obtaining FDA and other required regulatory  approvals is lengthy and expensive.
The time required for FDA approval is uncertain, and typically takes a number of
years,  depending  on the type,  complexity  and novelty of the  product.  Since
certain of our products  involve the  application  of new  technologies  and are
based on a new therapeutic  approach,  regulatory approvals may be obtained more
slowly  than  for  products  produced  using  more  conventional   technologies.
Additionally,  we may encounter  delays or  disapprovals  based upon  additional
government regulation resulting from future legislation or administrative action
or changes in FDA or equivalent foreign regulatory policy made during the period
of product development and regulatory review.

     We may apply  for  approval  from MCA or other  European  Union  regulatory
agencies to  commercialize  our potential  immunogen to treat one or more of the
gastrointestinal  system cancers and ulcerations previously described,  prior to
applying for similar FDA  approval.  Even if we obtain  approval from the MCA or
other foreign regulatory agencies, FDA approval would still be required prior to
marketing  such a  product  in the  United  States.  Although  we have  filed an
Investigational  New  Drug  application,  or IND (a type of  submission  used to
ultimately  obtain FDA approval to market a new drug),  with the FDA and the FDA
has  permitted  us to proceed  with  clinical  trials in the  United  States for
pancreatic cancer,  gastric cancer and prostate cancer, the clinical trials will
seek safety data as well as efficacy data and will require  substantial time and
significant  funding.  Furthermore,  we,  the  FDA,  the  MCA or  other  foreign
regulatory  agencies may suspend clinical trials at any time if it is determined
that the  participants in such trials are being exposed to  unacceptable  health
risks.  Approval  for any  products we develop may not be granted by  applicable
regulatory agencies on a timely basis, if at all, or if granted the approval may
not cover all the clinical  indications for which we are seeking approval or may
contain  significant  limitations  in  the  form  of  warnings,  precautions  or
contraindications with respect to conditions of use. Any delay in obtaining,  or
failure to obtain,  necessary  approvals would  adversely  affect our ability to
generate  product  revenue.  Failure to comply  with the  applicable  regulatory
requirements can, among other things, result in fines, suspensions of regulatory
approvals,  product recalls, operating restrictions and criminal prosecution. In
addition,  the marketing and manufacturing of drugs and biological  products are
subject to continuing  FDA review,  and later  discovery of  previously  unknown
problems with a product,  its manufacture or its marketing may result in the FDA
requiring  further  clinical  research  or  restrictions  on the  product or the
manufacturer, including withdrawal of the product from the market.

                                      -6-
<PAGE>

     The industry in which we operate is  characterized  by rapid  technological
change and intense competition. The treatment of diseases such as those to which
our  products are directed is subject to rapid,  unpredictable  and  significant
change.  Our products  under  development  seek to address  certain  cancers and
diseases currently  addressed,  to some extent, by existing or evolving products
and  technologies  of  other   biotechnology   and   pharmaceutical   companies.
Competition from other biotechnology  companies,  large pharmaceutical companies
and universities  and other research  institutions is intense and is expected to
increase.  Many of these companies and institutions have  substantially  greater
resources,  research and  development  staffs and facilities than we do and have
substantially  greater  experience  in  obtaining  regulatory  approval,  and in
manufacturing  and  marketing   pharmaceutical   products.  In  addition,  other
technologies  may in the  future  be the  basis  of  competitive  products.  Our
competitors  may succeed in developing  technologies  and products that are more
effective  than those we are  developing or that would render our technology and
products obsolete or noncompetitive.

     Our ability to enforce our patents and proprietary rights is uncertain. Our
success will depend in large part on our ability to obtain patents,  both in the
United States and in other countries,  maintain our unpatented trade secrets and
operate  without  infringing  on the  proprietary  rights of others.  The patent
positions of biotechnology and pharmaceutical  companies can be highly uncertain
and involve  complex  legal and factual  questions,  and  therefore the breadth,
validity and enforceability of claims allowed in patents we have obtained cannot
be predicted.

     As of March 31,  2003 we held 31 issued  patents  and have  pending  patent
applications and patent applications in preparation. Our pending applications or
patent  applications  in preparation  may or may not be issued as patents in the
future. Additionally,  our existing patents, patents pending and patents that we
may  subsequently  obtain  will  not  necessarily   preclude   competitors  from
developing  products that compete with products we have developed and thus would
substantially  lessen  the value of our  proprietary  rights.  We intend to file
additional patent applications, when appropriate,  relating to our technologies,
improvements to our technologies and specific products we may develop. If any of
our  patents  are   challenged,   invalidated,   circumvented   or  held  to  be
unenforceable, we could lose the protection of rights we believe to be valuable,
and our business could be materially and adversely affected.

     Our  commercial  success also will depend,  in part, on our not  infringing
patents  issued to others.  We may be  required  to obtain  licenses to patents,
patent  applications or other proprietary  rights of others. If we do not obtain
such  licenses,  we could  encounter  delays in product  introductions  while we
attempt to design around such patents,  or the development,  manufacture or sale
of products  requiring  such  licenses  could be  precluded.  Our  products  may
ultimately be found to infringe on the patents or proprietary  rights of others.
We could incur  substantial  costs,  including  diversion of management time, in
defending  ourselves  in  litigation  brought  against us on such  patents or in
litigation  in  which  we  assert  our  patents  against  another  party,  or in
litigation  brought by another party  asserting  its patents  against us. If our
competitors prepare and file patent applications in the United States that claim
technology  also  claimed  by us,  we may have to  participate  in  interference
proceedings  declared  by the U.S.  Patent  and  Trademark  Office to  determine
priority of invention,  which could result in substantial  financial costs to us
and diversion of management attention, even if the eventual outcome is favorable
to us. We believe  there  will  continue  to be  significant  litigation  in the
industry regarding patent and other intellectual property rights.

                                      -7-
<PAGE>

     We also rely on trade secrets to protect our technology,  especially  where
patent  protection is not believed to be appropriate  or obtainable.  We protect
our proprietary technology and processes, in part, by confidentiality agreements
with our employees,  consultants and certain  contractors.  These agreements may
not ultimately provide us with adequate protection.

     We depend on key  personnel.  We depend  upon the  services  of our  senior
management,  none of whom is subject to an employment agreement with us. We have
not insured against the loss, due to death or disability,  of any key personnel.
The loss of the  services  of any key  personnel  could have a material  adverse
effect on us.  Because of the  specialized  nature of our business,  our success
also depends upon our ability to attract and retain highly qualified  scientists
and other technical personnel.  We face intense competition for such persons and
we may not be able to attract or retain such individuals.

     We may be exposed to product  liability  claims and uninsured risk. The use
of  any  of  our  products,   whether  for  commercial  applications  or  during
pre-clinical  or  clinical  trials,  exposes us to an  inherent  risk of product
liability  claims if such  products  cause injury or result in adverse  effects.
Such   liability   might  result  from  claims  made  directly  by  health  care
institutions, contract laboratories or others selling or using such products. We
currently  maintain  product  liability  coverage  against risks associated with
testing our  potential  products  in clinical  trials.  Insurance  coverage  for
product liability,  however, is becoming increasingly expensive and difficult to
obtain.  Insurance  coverage may not be available in the future at an acceptable
cost, if at all, or in sufficient  amounts to protect us against such liability.
The  obligation  to pay any  product  liability  claim  in  excess  of  whatever
insurance  we are able to acquire  could have a material  adverse  effect on our
business, financial condition and future prospects.

     Our business  involves the use of hazardous  materials that could expose us
to environmental  liability. Our research and development activities involve the
controlled  use  of  hazardous  materials,   chemicals,   cultures  and  various
radioactive  compounds.  We are  subject  to  federal,  state and local laws and
regulations governing the use, generation,  manufacture,  storage, air emission,
effluent  discharge,  handling and disposal of such  materials and certain waste
products.  Although  we believe  that our safety  procedures  for  handling  and
disposing of such  materials  comply with the standards  prescribed by such laws
and  regulations,  the risk of  accidental  contamination  or injury  from these
materials cannot be completely eliminated.  In the event of such an accident, we
could be held liable for any damages  that result and any such  liability  could
exceed our resources.  We may be required to incur  significant  costs to comply
with  environmental  laws and  regulations  in the  future.  Current  or  future
environmental  laws  or  regulations  could  materially   adversely  affect  our
business, financial condition and results of operations.

     We  depend  on  others  for  manufacturing   and  marketing.   We  have  no
manufacturing  facilities  for  commercial  production  of  our  products  under
development  and have no  experience  in marketing,  sales or  distribution.  We
intend to continue establishing  arrangements with and relying on third parties,
including  large  pharmaceutical  companies,  to manufacture,  market,  sell and
distribute  any product we  develop.  Although  we believe  that  parties to any
future  arrangements  will have an economic  incentive  to perform  successfully
their  contractual  responsibilities,  the amount and timing of  resources to be
dedicated to these  activities will not be within our control.  Such parties may
not perform their obligations as expected, we may not

                                      -8-
<PAGE>

derive  any  revenues  from such  arrangements  and our  reliance  on others for
manufacturing  products may result in unforeseen  problems with product  supply.
Should we encounter  delays or difficulties in establishing  relationships  with
manufacturers to produce,  package and distribute any product we develop, market
introduction and subsequent sales of such products would be adversely  affected.
Moreover,  contract  manufacturers  that we may use must adhere to current  good
manufacturing  practice  regulations  enforced by the FDA through its facilities
inspection  program.  If  these  facilities  cannot  pass a  pre-approval  plant
inspection,  any FDA  pre-market  approval of our  potential  products  would be
adversely affected.  Additionally,  these manufacturers are subject to continual
review and periodic  inspections by the FDA and discovery of previously  unknown
problems with a manufacturer  or facility may result in FDA  restrictions  which
could adversely affect the manufacture and marketing of our products.

     We depend on one of our  strategic  collaborators  to supply one of our key
materials.  Diphtheria Toxoid (DT) is a key material used in the development and
manufacture  of  several  of  our  therapeutic  vaccines.  We do  not  currently
manufacture DT and large quantities of DT suitable for human use are not readily
obtainable in the open market. We currently have a supply agreement with Aventis
Pasteur, one of the few manufacturers of DT in the world, for this material.  If
the supply of DT from  Aventis  Pasteur is disrupted  for any reason,  we may be
unable to obtain  sufficient  quantities  of DT on a timely  and  cost-effective
basis, if at all. This could result in increased costs,  delayed  development or
ultimately  unsuccessful  clinical  trials which could  materially and adversely
affect our ability to commercialize our products.

     Future healthcare reforms may adversely affect our financial  results.  The
levels  of  revenues  and  profitability  of  biotechnology  and  pharmaceutical
companies,   including  us,  may  be  affected  by  the  continuing  efforts  of
governmental  and  third-party  payors to  contain or reduce the costs of health
care through various means. For example, in certain foreign markets,  pricing or
profitability of prescription  pharmaceuticals is subject to government control.
In the United States, there have been, and we expect that there will continue to
be, a number of federal and state  proposals to control health care costs. It is
uncertain what  legislative  proposals,  if any, will be adopted or what actions
federal,  state or  third-party  payors may take in  response to any health care
reform proposals or legislation.  Further,  to the extent that such proposals or
reforms  have  an  adverse  effect  on our  business,  financial  condition  and
profitability or that of other  biotechnology or  pharmaceutical  companies that
are prospective  corporate partners for certain of our products,  our ability to
commercialize our products may be affected adversely.

     Our   success   depends   on   third   party   reimbursement.    Successful
commercialization  of our products  will depend in part on the  availability  of
adequate  reimbursement from third-party health care payors,  such as government
and private  health  insurers and other  organizations.  Third-party  payors are
increasingly   challenging  the  pricing  of  medical   products  and  services.
Significant  uncertainty exists as to the reimbursement status of newly approved
health care products.  Any product that we succeed in bringing to market may not
be eligible for  reimbursement  at a level which is  sufficient  to enable us to
achieve market  acceptance of our products or to maintain  appropriate  pricing.
Without  such  reimbursement,  the  market  for  our  products  may be  limited.
Significant  reductions in insurance coverage also may have an adverse effect on
our future operations.

                                      -9-
<PAGE>

     The price of our common  stock may be  volatile.  The  market  price of our
common  stock,  like that of securities of other  biotechnology  companies,  has
fluctuated  significantly  in recent  years and is  likely to  fluctuate  in the
future. Announcements regarding

     o    scientific discoveries,

     o    strategic partnerships or arrangements,

     o    technological innovations,

     o    litigation and governmental inquiries,

     o    commercial products,

     o    patents or proprietary rights,

     o    the progress of clinical trials,

     o    government regulation,

     o    public  concern  as to the  safety  of drugs  and  reliability  of our
          testing processes,

     o    general market conditions,

     o    fluctuations in financial performance from period to period,

     o    termination of strategic alliances,

     o    new financings, and

     o    ability to maintain Nasdaq listing requirements

may have a significant impact on the market price of our common stock.

     The exercise of outstanding  warrants,  the  conversion of our  convertible
notes and other rights to obtain additional shares could dilute the value of the
shares;  sales of substantial  amounts of our shares of common stock could cause
the  price to go down.  As of April 11,  2003,  we had  approximately  3,364,940
outstanding  warrants to purchase shares of our common stock expiring at various
dates through October 1, 2021, with exercise prices ranging from $1.91 to $18.25
per common stock. The convertible note issued to Aventis  Pharmaceuticals,  Inc.
on December 19, 2002 enables Aventis Pharmaceuticals,  Inc. to convert such note
into shares of our common stock based upon a price  substantially  equivalent to
the market price of our common stock at the time of  conversion.  Based upon the
market  price  of the  shares  of our  common  stock  on  April  11,  2003,  the
convertible  note was convertible  into  approximately  1,162,791  shares of our
common stock. In addition,  subject to shareholder approval,  the holders of the
convertible  notes and warrants issued on March 31, 2003 will be able to convert
such notes into approximately 6,000,000 shares of common stock and exercise such
warrants to purchase up to 1,080,000 shares of common stock,  subject to certain
adjustments

                                      -10-
<PAGE>

described below and customary  anti-dilution  protection.  The exercise of these
warrants and the conversion of these notes could result in dilution in the value
of the shares of our common stock  outstanding and the voting power  represented
thereby.

     Subject to shareholder approval, the notes and warrants issued on March 31,
2003 contain adjustment  provisions which may cause subsequent  issuances of our
common  stock or  securities  convertible  into our common  stock  issued  below
certain  price  levels to  result in the  issuance  of a  significant  number of
additional shares upon the conversion of the notes and exercise of the warrants.
Under the provisions of the notes, if on or prior to March 31, 2006, we issue or
sell any shares of our common stock or securities convertible into shares of our
common stock for a consideration per share less than the conversion price of the
notes  in  effect  immediately  prior  to such  issuance  or  sale (a  "Dilutive
Issuance"),  then immediately after such Dilutive Issuance, the conversion price
of the notes will be reduced to an amount equal to such lower  consideration for
which our shares of common stock were issued.  If any Dilutive  Issuance  occurs
after March 31, 2004 and prior to March 31, 2006, then the conversion price will
not be  adjusted  below a price equal to 80% of the  conversion  price in effect
immediately before the Dilutive Issuance.  If any Dilutive Issuance occurs on or
after March 31, 2006 and prior to March 31, 2008,  then  immediately  after such
issuance, the conversion price will be reduced to an amount equal to the product
of (x) the conversion price in effect immediately prior to the Dilutive Issuance
and (y) the quotient of (1) the sum of (I) the product of the  conversion  price
then in effect immediately before the Dilutive Issuance and the number of shares
of Common  Stock  outstanding  immediately  prior to such  issuance and (II) the
consideration,  if any,  received by the  Company  upon the  Dilutive  Issuance,
divided  by  (2)  the  product  of (I)  the  conversion  price  then  in  effect
immediately before the Dilutive Issuance multiplied by (II) the number of shares
of  Common  Stock   outstanding   immediately   after  the  Dilutive   Issuance.
Substantially similar anti-dilution provisions are applicable to the warrants.

     The  foregoing  does not apply to common stock issued or issuable by us (i)
in  connection  with any employee  benefit  plan which has been  approved by our
board of  directors,  pursuant  to which  our  securities  may be  issued to any
employee,  officer or director for services provided to us, (ii) upon conversion
of the  notes  or upon  exercise  of the  warrants  described  in the  foregoing
paragraph,  (iii) in  connection  with the payment of any  interest on the notes
described in the foregoing paragraph in the form of shares of common stock, (iv)
in connection with a strategic  partnership or joint venture in which there is a
significant  commercial  relationship  between us and a third party, the primary
purpose of which is not to raise  capital  in an amount  not to  exceed,  in the
aggregate, gross proceeds of $20,000,000 or an aggregate of 10,000,000 shares of
our common  stock,  (v)  pursuant  to a bona fide firm  commitment  underwritten
public offering with a nationally  recognized  underwriter which generates gross
proceeds in excess of  $45,000,000  (other than an  "at-the-market  offering" as
defined in Rule 415(a)(4)  under the Securities Act and "equity lines") and (vi)
upon conversion of any options or convertible  securities  which are outstanding
under any of our stock option plans on the day  immediately  preceding March 31,
2003, provided that the terms of such options or convertible  securities are not
amended, modified or changed on or after March 31, 2003. We may issue additional
capital  stock,  warrants  and/or  options to raise  capital in the future which
could result in  additional  dilution.  Additionally,  to attract and retain key
personnel, we may issue additional securities, including stock options.

                                      -11-
<PAGE>

     No  prediction  can be made as to the effect,  if any, that future sales of
shares of our common stock, or the  availability of shares for future sale, will
have on the market price of the common stock prevailing from time to time. Sales
of substantial  amounts of shares of our common stock in the public  market,  or
the perception that such sales could occur,  could  adversely  affect the market
price of the  common  stock  and may make it more  difficult  for us to sell our
equity  securities in the future at a time and price which we deem  appropriate.
Public or private sales of substantial  amounts of shares of our common stock by
persons or entities that have exercised  options and/or warrants could adversely
affect the prevailing market price of the shares of our common stock.

     The  securities  purchase  agreement  relating  to the $15  million  senior
convertible  notes imposes  operating  restrictions  on us, which may prevent us
from taking some corporate actions.  The securities  purchase agreement relating
to the senior  convertible  notes imposes  operating  restrictions  on us. These
restrictions will, among other things, limit our ability to:

     o    on  or  before   March  31,  2006,   incur  or  guarantee   additional
          indebtedness;

     o    redeem,  pay cash dividends or make other  distributions on our common
          stock; and

     o    create liens.

     In addition,  for a period of 18 months  following the issuance by us of an
additional  $5,000,000  principal  amount  of notes to a  holder  of the  senior
convertible  notes and  warrants  issued by us on March 31,  2003 or, if no such
additional  notes are issued,  then from May 31, 2003,  we are  restricted  from
issuing,  selling or exchanging,  (A) any shares of our common stock, (B) any of
our other equity  securities,  including without  limitation shares of preferred
stock, (C) any of our debt securities  (other than debt with no equity feature),
including without limitation any debt security which by its terms is convertible
into or exchangeable for any of our equity securities, (D) any of our securities
that are a combination of debt and equity,  or (E) any option,  warrant or other
right to subscribe for,  purchase or otherwise  acquire any such equity security
or any such debt  security,  unless in each case we shall have first  offered to
sell such securities to the holders of the March 2003 senior  convertible  notes
on the same terms.

     We cannot assure you that these  covenants  will not  adversely  affect our
ability to finance our future operations or capital needs or to pursue available
business  opportunities  or limit  our  ability  to plan for or react to  market
conditions  or meet  capital  needs or  otherwise  restrict  our  activities  or
business  plans. A breach of any of these covenants could result in a default in
respect of such  convertible  notes.  If a default  occurs,  the investors could
elect to declare all amounts,  together with accrued interest, to be immediately
due and payable, at a price equal to 110% of such amount due.

     If we cannot operate as a going  concern,  our stock price will decline and
you could lose your entire  investment.  We have  incurred  recurring  operating
losses since  inception and had a negative  working capital at December 31, 2002
of  approximately  $5.4 million.  Our independent  auditors added a paragraph to
their  opinion on the  consolidated  financial  statements  for the year  ending
December  31, 2002 with  respect to our ability to continue as a going  concern.
The  financial  statements  do  not  include  any  adjustments  to  reflect  the
financings completed

                                      -12-
<PAGE>

subsequent  to December 31, 2002.  Management  believes that the receipt and the
application  of  proceeds  from  these  financings,  including  the $15  million
financing  completed on March 31, 2003, the second $5 million  tranche we expect
to complete and our plan to reduce  spending to less than $16 million during the
next 12 months will allow us to operate into the first quarter of 2004,  without
any additional funds.

     If we are unable to reduce spending and/or our operating expenses increase,
we may need additional funds to operate our business. In the event we are unable
to secure additional funding, in order to preserve cash, we would be required to
further  reduce  expenditures,   effect  further  reductions  in  our  corporate
infrastructure,  or we may be  required  to  delay,  reduce  the  scope  of,  or
eliminate  one or more of our  research or  development  programs,  any of which
could have a material  adverse  effect on our  ability to  continue  our current
level of operations.  Even if we obtain  additional  working capital in the near
future,  to the extent that operating  expenses  increase or we need  additional
funds to  develop  new  technologies,  the need for  additional  funding  may be
accelerated  and there can be no assurance that such  additional  funding can be
obtained  on terms  acceptable  to us, if at all. If we are not able to generate
sufficient capital through additional  financing to fund our current operations,
we may not be able to continue as a going concern.  If we are unable to continue
as a going  concern,  we may be  forced  to  significantly  reduce  or cease our
current operations. This could significantly reduce the value of our securities,
which could result in our delisting from Nasdaq and cause investment  losses for
our stockholders.

     We may not be able to maintain the Nasdaq listing requirements.  On October
15,  2002 and on November 1, 2002,  we  received  notices  from the staff of the
Nasdaq  National  Market that our common  stock had failed to  maintain  certain
minimum  requirements  for continued  listing on the Nasdaq  National Market and
both of the notices  suggested that we may want to consider applying to transfer
our securities to the Nasdaq Smallcap Market.  We were  subsequently  advised by
Nasdaq that we had regained  compliance  with certain minimum  requirements  for
continued  listing on the Nasdaq National Market and that our common stock would
continue to be listed on the Nasdaq National Market, pending future review.

Because  our  share  price  is  below  $3 per  share,  we are  currently  not in
compliance with the continued listing requirements of the Nasdaq National Market
and as a result our common stock may be  delisted.  In the event that our common
stock is delisted from the Nasdaq  National  Market,  we would apply to list our
common  shares  on the  Nasdaq  Smallcap  Market.  Even  if we had to  move  our
securities from the Nasdaq National  Market,  we believe that we satisfy all the
criteria for listing our common stock on the Nasdaq Smallcap Market which, among
others,  requires  that our  share  price  not  fall  below  $1.00.  There is no
assurance,  however,  that our  application  for trading our common stock on the
Nasdaq Smallcap Market would be accepted or, if accepted,  that we would be able
to maintain  eligibility for continued listing on the Nasdaq Smallcap Market. If
our common  stock were to be delisted  from the Nasdaq  National  Market and not
accepted for listing on the Nasdaq Smallcap  Market,  it could adversely  affect
our ability to raise funds through stock and debt issuances.

                                      -13-
<PAGE>

                           FORWARD-LOOKING STATEMENTS

     This prospectus,  any prospectus supplement and the documents  incorporated
by reference in this prospectus may contain forward-looking  statements. We have
based  these   forward-looking   statements  on  our  current  expectations  and
projections about future events.

     These statements include, but are not limited to:

     o    expectations  as to the adequacy of our cash balances,  cash flow from
          operations  and the  proceeds of  securities  issuances to support our
          operations  for  specified  periods  of time and as to the  nature and
          level of cash expenditures;

     o    expectations as to the receipt and timing of regulatory  clearance and
          approvals;

     o    expectations  as to the  development  of our  products,  including our
          clinical research program;

     o    statements as to anticipated reimbursement from third-party healthcare
          payors for our products;

     o    expectations as to the maintenance of the Nasdaq listing requirements;
          and

     o    expectations as to our ability to continue as a going concern.

     The  forward-looking  statements  included or  incorporated by reference in
these  documents  are  based  on  the  beliefs  of our  management  as  well  as
assumptions made by us and information  available to us on the date hereof.  Our
actual  results  could  differ   materially  from  those  anticipated  in  these
forward-looking  statements  as a result of various  factors,  including all the
risks discussed in "Risk Factors" and elsewhere in this prospectus.

     In addition,  statements that use the terms  "believe,"  "expect,"  "plan,"
"intend,"  "estimate,"  "anticipate"  and similar  expressions  are  intended to
identify  forward-looking  statements.  All  forward-looking  statements in this
prospectus  reflect  our  current  views  about  future  events and are based on
assumptions  and are  subject to risks and  uncertainties  that could  cause our
actual results to differ  materially from future results expressed or implied by
the forward-looking  statements. Many of these factors are beyond our ability to
control or predict.  You should not put undue  reliance  on any  forward-looking
statements.  We undertake no  obligation  to release  publicly any  revisions to
these  forward-looking  statements to reflect events or circumstances  after the
date of this  document or to reflect the  occurrence  of  unanticipated  events,
except as may be required under  applicable  securities  laws. In evaluating our
business,  you should  consider  carefully the factors set forth above under the
heading "Risk  Factors" in addition to the other  information  set forth in this
prospectus and incorporated by reference in this prospectus.

                                      -14-
<PAGE>

                                 USE OF PROCEEDS


     We will not receive any proceeds  from the sale of the shares of our common
stock by the  selling  stockholder,  if it chooses to sell some of the shares of
our common stock.

                             THE SELLING STOCKHOLDER

     On February 24, 2003, we entered into a Securities  Purchase Agreement with
the selling  stockholder and sold 500,000 shares of registered common stock from
our shelf Registration  Statement on Form S-3 at $2.96 per share (the average of
the closing bid prices of the common stock for the five days preceding  pricing)
for gross proceeds of $1,480,000.  Concurrently, we sold the selling stockholder
150,000  unregistered  warrants  at $0.125 per  warrant  for gross  proceeds  of
$18,750.  We issued all of the warrants under an exemption from the registration
requirements  of the Securities Act of 1933, as amended,  or the Securities Act,
pursuant to Section 4(2) of the  Securities  Act and/or Rule 506 of Regulation D
under the  Securities  Act. The warrants  were issued on February 24, 2003.  The
warrants are exercisable  from the date of issuance until February 24, 2008. The
holders of the warrants, upon exercise, may purchase a share of our common stock
at a price of $2.96 per share.  All of the  shares of common  stock to be issued
upon the  exercise  of the  warrants  issued  to the  investors  are  restricted
securities until we register them under this prospectus.

     The  following  table sets forth  information  known to us with  respect to
beneficial  ownership  of our common  stock as of April 11,  2003 by the selling
stockholder.  The number of shares in the column  "Shares  Which May Be Offered"
represents all of the shares that the selling  stockholder  may offer under this
prospectus.  The following table assumes that the selling  stockholder sells all
of the shares registered for sale under this prospectus. The selling stockholder
may sell some,  all or none of its  shares.  We do not know how long the selling
stockholder  will hold the shares before  selling them and we currently  have no
agreements,   arrangements  or  understandings   with  the  selling  stockholder
regarding the sale of any of the shares.

     Except as described in this prospectus, the selling stockholder has not had
a material  relationship  with us or any of our affiliates within the past three
years.

     In the following  table,  we have  determined  the number and percentage of
shares  beneficially  owned in  accordance  with  Rule  13d-3 of the  Securities
Exchange Act of 1934, as amended, or the Exchange Act, and this information does
not  necessarily  indicate  beneficial  ownership  for  any  other  purpose.  In
determining  the  number  of  shares  beneficially  owned  by a  person  and the
percentage  ownership  of that  person,  we  include  any shares as to which the
person  has sole or shared  voting  power or  investment  power,  as well as any
shares of our common  stock  subject to options,  warrants  or other  derivative
securities  held by that person that are currently  exercisable  or  exercisable
within 60 days after April 14, 2003. To our  knowledge,  the person named in the
table below has sole voting and  investment  power with respect to all shares of
our common stock shown as  beneficially  owned by it. The  percentage  of shares
owned in the following table are based on 24,851,639 shares of our common stock

                                      -15-
<PAGE>

outstanding,  giving  effect  to the  sale  of  150,000  shares  to the  selling
stockholder upon the exercise of the unregistered warrants.

     The  following  table sets  forth the number of shares of our common  stock
owned by the selling stockholder as of the date of this prospectus.

Selling Stockholder     Common stock           Common stock      Percentage of
                        beneficially owned     which may be      Common stock
                        prior to the           offered           held after sale
                        Offering                                 Common stock

Mainfield Enterprises   4,881                  150,000           0.62%
Inc.

Registration Rights of the Selling Stockholder

     Pursuant to a Registration Rights Agreement, dated as of February 24, 2003,
between  us and  the  selling  stockholder,  we  have  agreed  to  maintain  the
effectiveness  of the  Registration  Statement of which this prospectus  forms a
part  until the  earliest  to occur of (i) the date that is two years  after the
effective date of the  Registration  Statement of which this prospectus  forms a
part;  (ii) such time as all of the shares of our common stock have been sold by
the selling  stockholder;  and (iii) such time as the shares of our common stock
are eligible for resale pursuant to Rule 144 under the Securities Act.

                              PLAN OF DISTRIBUTION

     The  selling   stockholder   and  any  of  its   pledgees,   assignees  and
successors-in-interest, may, from time to time, sell any or all of its 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  stockholder  may  use  any one or more of the
following methods when selling shares:

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

-    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;

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

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

-    privately negotiated transactions;

                                      -16-
<PAGE>

-    short sales;

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

-    a combination of any such methods of sale; and

-    any other method permitted pursuant to applicable law.

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

     Broker-dealers  engaged by the  selling  stockholder  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  securities,  from the  purchaser)  in amounts to be
negotiated.  The  selling  stockholder  does not expect  these  commissions  and
discounts to exceed what is customary in the types of transactions involved.

     The  selling  stockholder  may from time to time pledge or grant a security
interest  in some or all of the common  stock or warrant  owned by it and, if it
defaults in the performance of its secured obligations,  the pledgees or secured
parties  may offer and sell the  shares of our  common  stock  from time to time
under this  prospectus,  or under an  amendment  to this  prospectus  under Rule
424(b)(3) or other applicable  provision of the Securities Act amending the list
of selling  stockholders to include the pledgee,  transferee or other successors
in interest as selling stockholders under this prospectus.

     The selling  stockholder  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.

     The selling  stockholder and any broker-dealers or agents that are involved
in selling the shares 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  purchased  by them  may be  deemed  to be  underwriting  commissions  or
discounts under the Securities Act. The selling stockholder has informed us that
it does not have any agreement or  understanding,  directly or indirectly,  with
any person to distribute the common stock.

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

                                  LEGAL MATTERS

     Certain legal matters with respect to the  securities  offered  pursuant to
this  Registration  Statement will be passed upon by White & Case LLP, New York,
New York.

                                      -17-
<PAGE>

                                     EXPERTS

     The  financial  statements  of  Aphton  Corporation   appearing  in  Aphton
Corporation's  Annual  Report (Form 10-K) for the year ended  December 31, 2002,
have  been  audited  by  Ernst  &  Young  LLP,   independent   certified  public
accountants, as set forth in their reports thereon (which contain an explanatory
paragraph describing conditions that raise substantial doubt about the Company's
ability to continue as a going  concern as described in Note 1 to the  financial
statements)  included  therein  and  incorporated  herein  by  reference.   Such
financial  statements are incorporated herein by reference in reliance upon such
report  given  on the  authority  of such  firm as  experts  in  accounting  and
auditing.

                       WHERE YOU CAN FIND MORE INFORMATION

     We  are  subject  to  the  informational   reporting  requirements  of  the
Securities  Exchange Act of 1934,  as amended,  and  therefore we file  reports,
proxy statements and other information with the SEC. You may read and copy these
reports and other information at the Public Reference Room maintained by the SEC
at 450 Fifth  Street,  N.W.,  Washington,  D.C.  20549.  Please  call the SEC at
1-800-SEC-0330  for  further  information  on the  public  reference  rooms.  In
addition,  the SEC  maintains a home page on the  Internet  (http://www.sec.gov)
that contains certain reports and other information filed by us.

                     INCORPORATION OF DOCUMENTS BY REFERENCE

     The SEC allows us to  "incorporate  by  reference"  information  from other
documents  that we file with them,  which means that we can  disclose  important
information by referring to those  documents.  The  information  incorporated by
reference is considered to be part of this  prospectus,  and information that we
file  later  with  the  SEC  will   automatically   update  and  supersede  this
information.

     This prospectus incorporates by reference the documents listed below.

     o    Annual Report on Form 10-K for the Fiscal Year Ended December 31, 2002
          filed on March 31, 2003;
     o    Current Reports on Form 8-K filed on February 6, 2003 and February 21,
          2003;  two  current  reports on Form 8-K filed on February  24,  2003;
          current report on Form 8-K filed on March 6, 2003; two current reports
          on Form 8-K filed on March 31, 2003;  and two current  reports on Form
          8-K filed on April 1, 2003; and
     o    The  description  of our common stock  contained  in our  Registration
          Statement on Form 8-A, filed on January 30, 1998.

     We also incorporate by reference additional documents that we may file with
the SEC under Section 13(a),  13(c), 14 or 15(d) of the Securities  Exchange Act
after the date of this prospectus and prior to the entire time all of the shares
of our common stock offered by this prospectus are sold.  These include periodic
reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and
Current Reports on Form 8-K, as well as proxy statements.

                                      -18-
<PAGE>

     We  undertake  to provide  without  charge to each  person,  including  any
beneficial owner, to whom a prospectus is delivered, a copy of these filings, at
no cost, by writing or telephoning us. Any requests should be directed to:

                               Aphton Corporation
                        80 S.W. Eighth Street, Suite 2160
                              Miami, Florida 33130
                               Tel: (305) 374-7338

     You  should  rely only on the  information  incorporated  by  reference  or
provided in this  prospectus or any  supplement.  We have not authorized  anyone
else to provide you with different  information.  You should not assume that the
information  in this  prospectus  or any  supplement  is accurate as of any date
other than the date on the front of those documents.

                                      -19-
<PAGE>

                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.*

         SEC registration fee.................................$      31.31
         Legal fees and expenses..............................$  40,000.00
         Accounting fees and expenses.........................$  10,000.00
         Miscellaneous........................................$     967.69
                                                               --------------
         Total................................................$  51,000.00
                                                               ==============

* All amounts are estimated.

Item 15. Indemnification of Directors and Officers.

     Section 145 of the Delaware  General  Corporation  Law (the "DGCL") permits
the Company to indemnify any person who is or was a director,  officer, employee
and agent,  or is or was  serving at the  request of the  Company as a director,
officer, employee or agent of another company, partnership, joint venture, trust
or other  enterprise  (each  an  "Insider")  against  liability  for  each  such
Insider's  acts taken in his or her  capacity  as an Insider in a civil  action,
suit or  proceeding  if such  actions  were  taken in good faith and in a manner
which  the  Insider  reasonably  believed  to be in or not  opposed  to the best
interests of the Company,  and in a criminal action, suit or proceeding,  if the
Insider had no  reasonable  cause to believe  his or her  conduct was  unlawful,
including under certain  circumstances,  suits by or in the right of the Company
for any expenses,  including attorneys' fees, judgments,  fines and amounts paid
in settlements  and for any  liabilities  which the Insider may have incurred in
consequence of such action,  suit or proceeding under conditions  stated in said
Section 145. The Company's Certificate of Incorporation and By-Laws provide that
the Company shall  indemnify  its  directors and officers to the fullest  extent
authorized  by the DGCL;  provided,  that the  Company  will not be  required to
indemnify  any director or  executive  officer in  connection  with a proceeding
initiated by such person, with certain exceptions.

     As  permitted  by  Section  102(b)(7)  of the  DGCL,  Article  NINTH of the
Company's  Certificate of Incorporation  provides that a director of the Company
will not be personally  liable to the Company or its  stockholders  for monetary
damages for breach of fiduciary duty as a director, except for liability (i) for
any breach of the director's duty of loyalty to the Company or its stockholders,
(ii) for acts or  omissions  not in good  faith  or  which  involve  intentional
misconduct or a knowing  violation of law,  (iii) under Section 174 of the DGCL,
as amended,  which concerns unlawful  payments of dividends,  stock purchases or
redemption,  or (iv) for any  transaction  from  which the  director  derived an
improper personal benefit.

     The Company's  Certificate of  Incorporation  permits the Company to secure
insurance on behalf of any director,  officer,  employee or agent of the Company
or another Company,  partnership,  joint venture,  trust or other enterprise for
any liability arising out of his or her actions in such capacity,  regardless of
whether the Company would have the power to indemnify  such person  against such
liability under the DGCL.

                                      -20-
<PAGE>

Item 16. Exhibits.

       Exhibit No.                       Description

           4.1           Warrant to purchase  Common Stock,  dated February
                         24,  2003,   issued  by  Aphton   Corporation   to
                         Mainfield   Enterprises   Inc.   (incorporated  by
                         reference  to the  Registrant's  Annual  Report on
                         Form 10-K  filed for the year ended  December  31,
                         2002, filed on March 31, 2003).

           5.1           Opinion of White & Case LLP.

          23.1           Consent of independent certified public accountants,
                         Ernst & Young LLP.

          23.2           Consent  of  White  & Case  LLP  (included  in  their
                         opinion filed as Exhibit 5.1 hereto).

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

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

Item 17. Undertakings.

(a)  The undersigned Registrant hereby undertakes:

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

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

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

                                      -21-
<PAGE>

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

          provided,  however,  that  paragraphs  (a)(1)(i) and (a)(1)(ii) do not
          apply if the information  required to be included in a  post-effective
          amendment by those  paragraphs is contained in periodic  reports filed
          with or  furnished to the  Commission  by the  Registrant  pursuant to
          Section  13 or 15(d) of the  Exchange  Act  that are  incorporated  by
          reference in the Registration Statement.

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

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

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

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

(d)  The undersigned Registrant hereby undertakes that:

     (1)  For purposes of determining  any liability  under the Securities  Act,
          the information  omitted from the form of prospectus  filed as part of
          this  Registration  Statement in reliance upon Rule 430A and contained
          in a form of  prospectus  filed  by the  Registrant  pursuant  to Rule
          424(b)(1) or (4) or 497(h) under the Securities Act

                                      -22-
<PAGE>

          shall be deemed to be part of this  Registration  Statement  as of the
          time it was declared effective.

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


                                      -23-
<PAGE>

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, as amended, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-3 and has duly caused this Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized, in the City of New York, New York, on the 14th day of April, 2003.

                                      APHTON CORPORATION

                                      By:/S/ PHILIP C. GEVAS
                                         ---------------------------------------
                                         Philip C. Gevas
                                         Chairman, President and Chief Executive
                                         Officer

                                POWER OF ATTORNEY

     KNOW ALL PERSONS BY THESE  PRESENTS,  each person whose  signature  appears
below  constitutes  and appoints  Philip C. Gevas and Frederick W. Jacobs as his
true and  lawful  attorneys-in-fact,  each  acting  alone,  with  full  power of
substitution  and  resubstitution,  for such  person and in his name,  place and
stead  in any  and all  capacities,  to sign  any or all  amendments  (including
post-effective amendments) to this Registration Statement, and to file the same,
with  exhibits  thereto and other  documents in connection  therewith,  with the
Securities and Exchange Commission,  granting unto said  attorneys-in-fact  full
power and authority to do and perform each and every act and thing requisite and
necessary  to be done in and about the  premises,  as fully for all  intents and
purposes as he might or could do in person,  hereby ratifying and confirming all
that each of said attorneys-in-fact,  or their substitute or substitutes, may do
or cause to be done by virtue hereof.

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

                                      -24-
<PAGE>

<TABLE>
<CAPTION>

                Signature                                  Title                               Date
                ---------                                  -----                               ----

<S>                                        <C>                                            <C>
                                           Chairman, President and Chief                  April 14, 2003
/S/  PHILIP C. GEVAS                       Executive Officer
--------------------------------------
Philip C. Gevas

/S/  WILLIAM A. HASLER                     Vice Chairman of the Board, Director           April 14, 2003
--------------------------------------     and Co-Chief Executive Officer
William A. Hasler

/S/  NICHOLAS JOHN STATHIS                 Director                                       April 14, 2003
--------------------------------------
Nicholas John Stathis

/S/  GEORGES HIBON                         Director                                       April 14, 2003
--------------------------------------
Georges Hibon

/S/  FREDERICK W. JACOBS                   Vice President, Chief Financial                April 14, 2003
--------------------------------------     Officer,Treasurer and Chief
Frederick W. Jacobs                        Accounting Officer

</TABLE>