***Text Omitted and Filed Separately
                                                Confidential Treatment Requested
                                             Under 17 C.F.R. ss.ss. 22.80(b)(4),
                                                               200.83 and 240b-2




 [Letterhead of SCHERING CORPORATION]


                                                               December 15, 1998

 Mr. Randall E. Woods
 President and Chief Executive Officer
 Corvas International, Inc.
 3030 Science Park Road
 San Diego, California 92121

 RE: Factor Xa Research Programs

 Dear Mr. Woods:

         This "Letter of Agreement" is to notify you of Schering's decision to
 extend the term of the Factor Xa Research Program under the Agreement by and
 between Corvas International, Inc. ("Corvas") and Schering Corporation and
 Schering-Plough Ltd. (collectively "Schering"), effective as of December 14,
 1994 (the "Agreement"), subject to the following modifications.

         1.       The Factor Xa Research Program shall be extended for a period
                  of nine (9) months, i.e., from January 14, 1999 through
                  September 14, 1999 (the "Extension").

         2.       Schering shall pay to Corvas three million dollars
                  ($3,000,000) in research funding for the Extension, such
                  payment to be made in three (3) equal quarterly payments, the
                  first to be made on or before January 14, 1999, and the
                  remaining amounts payable on or before April 14, 1999 and July
                  14, 1999.

         3.       Corvas shall provide staffing for the Factor Xa Research
                  Program at a level of [...***...] FTEs (consisting of
                  [...***...] chemists and [...***...] biologists) during this
                  Extension.



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* CONFIDENTIAL TREATMENT REQUESTED



<PAGE>



                                            ***Text Omitted and Filed Separately
                                                Confidential Treatment Requested
                                             Under 17 C.F.R. ss.ss. 22.80(b)(4),
                                                               200.83 and 240b-2


                                       -2-

Mr. Randall E. Woods                                 December 15, 1998

         4.       Corvas shall, at Corvas' expense, perform (or out-source) the
                  in vivo pharmacokinetic testing in dogs of potential lead
                  compounds arising from research conducted during the
                  Extension.

         5.       Schering shall, at its sole discretion and at its expense,
                  perform pharmacological efficacy studies to evaluate the
                  antithrombotic potential of selected compounds during or after
                  the Extension.

         6.       The goal of the Extension shall be to discover [...***...]
                  small molecule anticoagulant that specifically inhibits either
                  thrombin, Factor Xa, or both, and has additional properties
                  characteristic of a clinical development candidate. The
                  characteristics of such a development candidate shall be
                  defined by the parties based upon the Acceptance Criteria set
                  forth in the Agreement, as modified by mutual agreement of the
                  parties.

         7.       The terms and conditions of the Agreement shall be amended to
                  include expansion of the licenses granted in Article 2 of the
                  Agreement to reflect the expansion of the research
                  collaboration to include both Thrombin Inhibitors and Factor
                  Xa Inhibitors.

         8.       Corvas agrees to give good faith consideration to Schering's
                  request that Schering retain rights for a period of three (3)
                  years after the expiration of the Extension and termination of
                  the Agreement to compounds discovered/ developed during the
                  Extension.

         9.       Schering agrees to give good faith consideration to Corvas'
                  request that the rights to NAP5 be returned to Corvas.



-------------------------
* CONFIDENTIAL TREATMENT REQUESTED



<PAGE>



                                            ***Text Omitted and Filed Separately
                                                Confidential Treatment Requested
                                             Under 17 C.F.R. ss.ss. 22.80(b)(4),
                                                               200.83 and 240b-2


                                       -3-

Mr. Randall E. Woods                                 December 15, 1998

         10.      Sixty (60) days prior to the expiration of the Extension, the
                  parties shall discuss extending the term of the oral
                  anticoagulant research collaboration between Corvas and
                  Schering. Notwithstanding anything in the Agreement to the
                  contrary, neither party shall have the right to unilaterally
                  renew or extend the term of the research collaboration.

         11.      In the event that during the Extension Schering accepts one or
                  more compounds as a clinical development candidate, then it
                  shall have the right to continue the development and
                  commercialization of such compound(s) in accordance with the
                  terms of the Agreement, including as it may be amended
                  pursuant to this Letter of Agreement, provided that Schering's
                  diligence obligations with respect to such compound(s) shall
                  be essentially as those set forth in Article 4 of the
                  Agreement.

         12.      The parties shall agree upon additional amendments to the
                  terms of the Agreement to reflect the terms agreed upon for
                  the Extension as contemplated hereunder.

         Pursuant to Section 4. 1A of the Agreement, Schering and Corvas shall
 amend Exhibit G of the Agreement to set forth the responsibilities of the
 parties with respect to performance of the research collaboration during the
 Extension.

         The good faith negotiation of amendments to the Agreement and Exhibit
 G, and the matters set forth in Sections 8 and 9 above, is to be completed
 within thirty (30) days of the date on which Corvas receives this Letter of
 Agreement.

         We at Schering look forward to continuing our collaborative research
efforts under the Agreement.



<PAGE>



                                            ***Text Omitted and Filed Separately
                                                Confidential Treatment Requested
                                             Under 17 C.F.R. ss.ss. 22.80(b)(4),
                                                               200.83 and 240b-2


                                       -4-

Mr. Randall E. Woods                                 December 15, 1998

         Please indicate Corvas' acceptance and agreement to the provisions set
 forth in this Letter of Agreement by signing below on behalf of Corvas and
 returning one signed original to Schering.

 Very truly yours,         LEGAL REVIEW                       LEGAL REVIEW

Schering Corporation                              Schering-Plough, Ltd.



/s/ DAVID POORVIN                                  /s/ DAVID POORVIN
---------------------                              ---------------------
David Poorvin, Ph.D.                               David Poorvin, Ph.D.
Vice President                                     Prokurist




 Acknowledged and Agreed to

 Corvas International, Inc.

 By: /s/ RANDALL E. WOODS
     --------------------
 Date: December 15, 1998
       -----------------

 cc:     Corporate Secretary, Corvas International
         Cooley Godward LLP
         Cecil B. Pickett, Ph.D.
         Ashit Ganguly, Ph.D.
         Richard Chipkin, Ph.D.