EXHIBIT 99.1



                  CERTIFICATION BY PRINCIPAL EXECUTIVE OFFICER
                       PURSUANT TO 18 U.S.C. SECTION 1350,
                       AS ADOPTED PURSUANT TO SECTION 906
                        OF THE SARBANES-OXLEY ACT OF 2002


         In connection with the accompanying Annual Report on Form 10-K of
Ligand Pharmaceuticals Inc. for the year ended December 31, 2002, I, David E.
Robinson, Chairman, President and Chief Executive Officer of Ligand
Pharmaceuticals Inc., hereby certify pursuant to 18 U.S.C. Section 1350, as
adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, to the best
of my knowledge and belief, that:

         (1) such Annual Report on Form 10-K for the year ended December 31,
2002, fully complies with the requirements of section 13(a) or 15(d) of the
Securities Exchange Act of 1934; and

         (2) the information contained in such Annual Report on Form 10-K for
the year ended December 31, 2002, fairly presents, in all material respects, the
financial condition and results of operations of Ligand Pharmaceuticals Inc.



Date:  March 21, 2003           /S/DAVID E. ROBINSON
                                --------------------------------
                                David E. Robinson
                                CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER