***TEXT OMITTED AND FILED SEPARATELY
                                                CONFIDENTIAL TREATMENT REQUESTED
                                             UNDER 17 C.F.R. SS.SS. 22.80(b)(4),
                                                               200.83 AND 240b-2

                               AMENDMENT AGREEMENT
                               -------------------

         This Amendment Agreement ("Amendment") effective as of the last date on
the signature page hereof (the "Amendment Date"), by and between Corvas
International, Inc. ("Corvas") and Schering Corporation and Schering-Plough Ltd.
(collectively "Schering") amends and supplements the Collaboration and License
Agreements among Corvas and Schering effective as of June 11, 1997 (the
"Agreement").

         WHEREAS, the parties, as of March 31, 2000 have suspended, and now
desire to terminate the Research Program Term prior to its normal expiration on
the third anniversary of the Effective Date; and

         WHEREAS, the parties wish to clarify their respective rights and
obligations with regard to certain compounds and related intellectual property
generated either solely or jointly by Corvas and/or Schering; and

         WHEREAS, Corvas desires to grant to Schering certain additional rights
with regard to such compounds and intellectual property in exchange for certain
additional consideration to be paid by Schering,

         NOW THEREFORE, the parties agree to amend and supplement the terms of
the Agreement as follows:

         Except as expressly defined herein all capitalized terms used in this
Amendment shall have the meanings set forth in the Agreement.

1. The parties acknowledge that as of the Amendment Date, all of the compounds
(including, without limitation, HCV Activity Compounds and/or Candidate
Compounds) which are Corvas Inventions, Schering Inventions and/or Joint
Inventions arising from the Research Program have been identified and will be
the subject of a series of patent applications constituting Corvas Patent Rights
and Schering Patent Rights to be filed by Schering as soon as practicable after
the Amendment Date. Promptly after such applications have been filed, Schering
shall provide Corvas with a schedule of those constituting Corvas Inventions or
Joint Inventions (Appendix 1) and a separate schedule of those constituting
Schering Inventions (Appendix 2).

2. Notwithstanding anything in the Agreement to the contrary, Corvas hereby
grants to Schering an exclusive (even as to Corvas) license, with the right to
grant sublicenses, under the Corvas Patent Rights related to Corvas Inventions
and Joint Inventions, and any Corvas Know-How directly related thereto, to make,
use, sell, offer for sale, import and export the compounds claimed by such
Corvas Patent Rights (including, without limitation, any HCV Activity Compounds
and/or Candidate Compounds), and any products containing such compounds, for any
and all uses in the Territory. Any products containing any such compounds which
are developed by or on behalf of Schering shall be deemed Licensed Products and
shall be subject to the royalty obligations set forth in Article 4 of the
Agreement.

                                       1.
<PAGE>

3. The parties acknowledge and agree that Schering shall hold all rights, title
and interest in and to (i) any compounds actually prepared by Schering during
the Research Program Term which are Schering Inventions, (the "Schering
Compounds"), and (ii) the Schering Patent Rights. Nothing in the Agreement or
this Amendment shall be construed as granting, either expressly or by
implication, to Corvas any license or other rights to any Schering Compounds,
Schering Patent Rights or other Schering know-how or intellectual property
rights which relate to the Schering Compounds.

4. The parties further acknowledge and agree that any products containing a
Schering Compound shall not be considered Licensed Products and that Schering
shall have no Earned Royalty payment obligations under Article 4 of the
Agreement with respect to Schering Compounds and/or such products. In addition,
Schering shall have no royalty payment obligations under the Agreement or this
Amendment with respect to any products containing compounds covered by the
Schering Patent Rights which are not Schering Compounds. However, with respect
to any products containing a Schering Compound which are developed and
commercialized for the treatment of hepatitis C virus, Schering shall pay to
Corvas a fixed royalty of: (i) [...***...], and (ii) [...***...]. Any royalty
payments due under this Paragraph 2 shall be paid quARTerly in accordance with
the terms of Sections 4.5, 4.7, 4.8, 4.9, 4.10 and 4.11 of the Agreement.

5. In consideration for the exclusive licenses under Corvas Patent Rights and
the other rights granted to Schering under this Amendment, Schering shall pay to
Corvas a license fee of two million five hundred thousand dollars ($2,500,000),
which payment shall be due within five (5) business days of the Amendment Date.

6. As of the Amendment Date Schering shall have no obligation to pay milestone
payments to Corvas in connection with the discovery and development of compounds
under the Agreement. Accordingly, Sections 4.2, 4.3 and 4.4 of the Agreement are
hereby deleted in their entirety.

7. The Research Program Term is hereby terminated effective as of March 31,
2000. As of that date, Corvas shall have no further obligation to perform the
Research Program and Schering shall have no further obligation to provide
research funding for the Research Program.

8. For a period of five (5) years from the Amendment Date, Corvas and its
Affiliates shall not perform any research and/or development activities, either
alone or in collaboration with any third party, with regard to hepatitis C viral
proteases.

9. Any new HCV protease inhibitor compounds discovered by Schering after the
expiration Research Program which are separately patentable ("New Compounds")
shall be deemed independent inventions outside the scope of the Agreement.
Notwithstanding anything in the Agreement or this Amendment to the contrary, the
parties acknowledge and agree that Schering shall have no obligations to Corvas
with respect to any New Compounds and/or products containing any New Compounds.



*CONFIDENTIAL TREATMENT REQUESTED

                                       2.
<PAGE>

10. Promptly after the Amendment Date, Corvas shall provide to Schering any
unused samples of any compounds prepared by Corvas in performance of the
Research Program, any reagents provided by Schering to Corvas for use in
performance of the Research Program, and/or any Schering Compounds, which are in
Corvas' possession.

11. The contributions made by Corvas' employees will be acknowledged in any
scientific publication or other public presentation of the results of the
Research Program.

         Except as expressly amended and supplemented hereby, all other terms of
the Agreement shall remain in full force and effect.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed in duplicate by their duly authorized representatives.

 CORVAS INTERNATIONAL, INC.                       SCHERING CORPORATION

BY: /S/ RANDALL E. WOODS                          BY: /S/ DAVID POORVIN
    -----------------------------------               --------------------
NAME: Randall E. Woods                                David Poorvin, Ph.D.
      ---------------------------------
TITLE: President & CEO                                Vice President
       ---------------------------------
DATE: 18 May 2000                                 DATE: 17 MAY 2000
      ----------------------------------                -----------


                                                  SCHERING-PLOUGH LTD.

                                                  BY: /S/ DAVID POORVIN
                                                      ---------------------
                                                      David Poorvin, Ph. D.
                                                      Prokurist

                                                  DATE: 17 MAY 2000
                                                        -----------

                                       3.
<PAGE>

                                   Appendix 1

                          CERTAIN CORVAS PATENT RIGHTS
                          ----------------------------


The following patent applications and any patents issuing therefrom, including
any provisionals, divisionals, continuations, continuations-in-part, reissues,
reexaminations, or extensions thereof, and any corresponding foreign patents,
are Corvas Patent Rights for purposes of paragraph 2 of the Amendment:

CORVAS INVENTIONS:
------------------

(to be provided)



JOINT INVENTIONS:
-----------------

(to be provided)

                                       4.
<PAGE>

                                   Appendix 2

                    PATENT RIGHTS CLAIMING SCHERING COMPOUNDS
                    -----------------------------------------


The following patent applications any patents issuing therefrom, including any
provisionals, divisionals, continuations, continuations-in-part, reissues,
reexaminations, or extensions thereof, and any corresponding foreign patents are
Schering Patent Rights for purposes of paragraph 3 of the Amendment:



SCHERING INVENTIONS:
--------------------

(to be provided)

                                       5.