AMENDMENT No 1 to the Collaboration and
      License Agreement and the Subscription Agreement dated June 12, 1998

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This Amendment  no 1 dated 10th May 2000  ("Amendment")  is made between Aphton
Corporation,  a company  organized under the laws of Delaware with its principal
executive  offices at World Trade Center,  80 SW Eight Street Suite 2160, Miami,
Florida  (hereinafter  "Aphton") and SmithKline  Beecham PLC,  having a place of
business at New Horizons Court, Great West Road,  Brentford,  Middlesex TW8 9EP,
United Kingdom (hereinafter "SB").

WHEREAS

       -      Aphton and SB entered into a Collaboration  and License  Agreement
              dated  June  12,  1998  ("the   Agreement")  for  the  purpose  of
              developing an anti-gonodotropin releasing hormone (GnRH) immunogen
              product for the  treatment  and  prevention  of  gonadotropin  and
              gonadal steroid hormone associated diseases and cancers in humans.

       -      Pursuant  to the  Agreement  SB and  Aphton  agreed  to  conduct a
              development plan funded by SB in accordance with a budget approved
              by the Steering Committee ("Development Plan").

       -      Parties  wish to amend such  Development  Plan and the sections of
              the Agreement  which govern the funding of the  Development  Plan.
              Once  Aphton  has  developed  an  antiGnRH  immunogen  ("lmmunogen
              Development  Program")  at its expense  which will be presented to
              the Steering Committee and provided SB accepts such immunogen,  SB
              shall be  responsible  for further  development  of the product in
              accordance  with the  Development  Plan, as amended and updated by
              the parties.

       -      Parties  further wish to amend the  principles  governing  the put
              option of Aphton as set forth in the Subscription Agreement.

          NOW,  THEREFORE,  on May 10, 2000 (hereafter the "Execution Date") the
parties hereto agree as follows:

          1. DEFINITIONS

          All  definitions  set forth in Section 1 of this Agreement shall apply
in full to this Amendment No. 1.

          2. DEVELOPMENT PROGRAM

          The following Section of Article 3 of the Agreement shall be amended:

<PAGE>

          3.1.(i)   SB  agrees  to  deliver   to  Aphton   anti-GnRH   conjugate
manufactured  under contract for SB (hereafter the "Conjugate") at no expense to
Aphton within sixty (60) days of the acceptance of an amended  Development  Plan
by the  Steering  Committee  (the date of said  delivery  hereafter  termed  the
"Delivery  Date").  The Steering  Committee  shall  either  accept or reject the
amended  Development Plan within thirty (30) days of submission by Aphton to the
Steering  Committee,  which shall happen no later than sixty (60) days after the
Execution Date. Such submission shall include the immunogen  development program
up to  presentation  by Aphton to the  Steering  Committee  in  accordance  with
Section 3.1(ii) below. SB shall deliver  quantities of the Conjugate  sufficient
to carry out the amended Development Plan as approved by the Steering Committee,
and  if so  decided  by the  Steering  Committee  SB  shall  deliver  reasonable
additional  quantities of the Conjugate as approved by the Steering Committee at
any later time. The parties agree to replace the  Development  Plan contained in
Schedule B of the Agreement  with the amended  Development  Plan, as approved by
the  Steering   Committee.   The  Development  Program  Term  shall  be  amended
accordingly.  Except  for the costs  associated  with the  manufacturing  of the
Conjugate,  Aphton shall be  responsible  for funding all costs for research and
development  relating  to  Aphton's  Product  (including  formulations  in  SB's
Adjuvant  Technology)  to be presented to the Steering  Committee in  accordance
with paragraph (ii) below.

          (ii) Aphton shall  present its Product to the Steering  Committee  for
acceptance. (The date on which Aphton first presents its Product to the Steering
Committee  shall  hereafter  be termed the  "Presentation  Date.") The  Steering
Committee  shall  have  sixty  (60) days to accept or reject  Aphton's  Product.
Failure by the Steering  Committee to either accept or reject  Aphton's  Product
within sixty (60) days of the Presentation  Date shall be considered a rejection
by the Steering  Committee.  If the Steering Committee rejects Aphton's Product,
the parties may agree that Aphton will be allowed to conduct additional research
and development and make a subsequent presentation to the Steering Committee for
acceptance.  In no event shall the Presentation  Date be later than [Redacted]*.
After the Steering Committee has accepted Aphton's Product (hereafter termed the
"Acceptance  Date"),  SB shall undertake the further  development of the Product
under the amended  Development  Plan (other than the immunogen  development) and
shall be  responsible  for  funding  all costs  (as  previously  defined  in the
Agreement).

          The Development  Program can be amended and/or  complemented from time
to time by the Steering Committee.

          Section 3.1(iv) shall be complemented as follows:

          During the Development  Program Term and any extension  thereof Aphton
undertakes to (i) use best efforts to materially  perform all its  activities in
the  Development  Program  (ii) and use all  reasonable  efforts to achieve  its
objectives under the Development Program.

          Section 3.1(v) shall be complemented as follows:

          "Aphton shall during the Development  Program Term refrain from adding
Third Party  technology  (including but not limited to Adjuvants) to the Product
without prior agreement hereto by the Steering Committee."

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*    The redacted  portions of this  document  have been  omitted  pursuant to a
     request for  confidential  treatment and such  redacted  portions have been
     filed separately with the Securities and Exchange Commission.

                                      -2-

<PAGE>

          Section 3.1(vii) of the Agreement shall be complemented as follows:

          "If the  Steering  Committee  decides that SB Adjuvant  Technology  is
required,  such  technology  shall  be made  available  under  the  terms of the
Material Transfer Agreement attached hereto as Schedule B.

          Section 3.2 of the Agreement shall be amended as follows:

          "In the event that SB's  funding  obligation  as  incurred  up to date
pursuant to the amended Article 3.2 of the Agreement of the amended  Development
Plan and any funding SB would incur at any moment in time under the  Development
Plan under this Amendment,  exceeds [Redacted]* per indication within the Field,
such portion  exceeding  [Redacted]*  per  indication  within the Field shall be
fully creditable against Aphton Royalties as set forth in Section 6.2.2.  and/or
the royalties  payable  under Section 6.5. For the avoidance of doubt,  prostate
cancer shall be  considered  as one (1)  indication,  regardless of the stage of
disease of the prostate cancer.

          13. TERM AND TERMINATION

          The following Section of Article 13 shall be amended:

          13.2 Termination by Either Party For Cause.  Upon occurrence of any of
the following,  either party may terminate this Agreement,  in whole or in part,
with respect to the Product:  (a) mutual agreement,  (b) material breach of this
Agreement provided that the non-breaching  party notifies the breaching party in
writing of such breach and the  breaching  party does not cure the breach within
60 days after receiving the notice and (c) liquidation, dissolution, winding-up,
insolvency,  bankruptcy,  or filing  any  petition  therefor,  appointment  of a
receiver,  custodian or trustee, or any other similar  proceeding,  by or of any
party.

          13.3 Termination by Right.

          13.3.1  Termination by SB. Prior to the Acceptance Date, SB shall have
the right to terminate this Agreement at the earlier of (a) eighteen (18) months
after the Delivery  Date  (defined in 3.1.(i)) or (b) as from  December 31, 2001
upon thirty (30) days prior notice to Aphton. Subsequent to the Acceptance Date,
SB shall  have the right to  terminate  this  Agreement  (i) prior to receipt of
regulatory approval,  upon sixty (60) days prior notice to Aphton, or (ii) after
regulatory approval,  upon one hundred eighty (180) days prior notice to Aphton,
in the event that SB determines at its sole discretion that for safety, efficacy
or economical  reasons it does not wish to promote,  market or sell the Product.
In such event, SB shall have no further obligation to Aphton, except as provided
in Section 13.4 hereof and Aphton shall have no further  obligation  to SB after
regulatory approval,  upon one hundred eighty (180) days prior notice to Aphton,
in the event that SB determines at its sole discretion that for safety, efficacy
or economical  reasons it does not wish to promote,  market or sell the Product.
In such event, SB shall have no further obligation to Aphton, except as provided
in Section 13.4 hereof and Aphton shall have no further obligation to SB.

          13.3.2  Termination by Right by Aphton.  Prior to the Acceptance  Date
and after the Presentation  Date,  Aphton shall have the right to terminate this
Agreement at any time upon thirty (30) days' notice to SB provided  that (i) the
Steering  Committee has rejected the Product

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*    The redacted  portions of this  document  have been  omitted  pursuant to a
     request for  confidential  treatment and such  redacted  portions have been
     filed separately with the Securities and Exchange Commission.

                                      -3-

<PAGE>

presented  by Aphton  and (ii) the  parties  do not agree  pursuant  to  Section
3.1(ii) within twenty (20) days after such  rejection by the Steering  Committee
that Aphton shall be allowed to make a subsequent  presentation.  If the parties
agree  that  Aphton  shall be allowed to make a  subsequent  presentation,  then
Aphton  shall  have the right to  terminate  the  Agreement  at any time after a
rejection  by the Steering  Committee of the Product  presented by Aphton at the
subsequent  presentation,  upon thirty (30) days notice to SB, and Aphton  shall
have no further obligation to SB.

          13.3.3 Upon  termination by SB, SB must transfer all Conjugate in SB's
possession to Aphton at no cost to Aphton.

          14. MISCELLANEOUS

          The following Sections of Article 14 shall be added:

          14.14. Put Option:  Section 3.1 of the Subscription Agreement attached
as Schedule C to the Agreement shall be amended as follows:

          14.14.1.   Notwithstanding  the  provisions  in  Section  3.1  of  the
Subscription  Agreement,  Aphton  shall not  exercise the Put Option at any time
prior to the Acceptance Date (as defined above).

          14.14.2. The Put Options Notice shall be sixty (60) days.

          14.15.  All other Articles and Sections  (including the other Sections
of Article 3 not referred to herein) shall remain in full force and effect.

                                      -4-

<PAGE>

          IN WITNESS  WHEREOF,  Aphton and SB have caused this  Agreement  to be
executed in duplicate  by their duly  authorized  representatives  as of the day
given above.

APHTON CORPORATION                    SMITHKLINE BEECHAM PLC



By: /s/ Philip C. Gevas               By: /s/ Jean Stephenne
   -------------------------------      ----------------------------------------
Name:  Philip C. Gevas                Name:  Jean Stephenne
Title: Chairman, President            Title: Attorney-in-Fact
       and Chief Executive Officer