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                                                                    EXHIBIT 99.1

                                  SERAGEN, INC.

               PROXY SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

        The undersigned hereby appoints ___________ and ___________ jointly and
severally as proxies, with full power of substitution and resubstitution, to
vote all shares of stock which the undersigned is entitled to vote at the
Special Meeting of Stockholders of Seragen, Inc. (the "Company") to be held on
________, 1998 (the "Special Meeting"), or at any adjournments or postponements
thereof, as specified below, and to vote in the proxyholders' discretion on such
other business as may properly come before the Special Meeting and any
adjournments or postponements thereof.

            THE BOARD OF DIRECTORS RECOMMENDS A VOTE FOR PROPOSAL 1.

1.      Approval of Merger. A proposal to approve and adopt the Agreement and
        Plan of Reorganization, dated May 11, 1998 (the "Merger Agreement"), by
        and among the Company, Ligand Pharmaceuticals Incorporated, a Delaware
        corporation ("Ligand"), and Knight Acquisition Corp., a Delaware
        corporation and a wholly owned subsidiary of Ligand ("Merger Sub"), and
        to approve Ligand's acquisition of the Company through the merger of
        Merger Sub with and into the Company, with the Company being the
        surviving corporation and becoming a wholly owned subsidiary of Ligand
        (the "Merger").

        [ ] FOR               [ ] AGAINST               [ ] ABSTAIN

        Unless otherwise specified by the undersigned, this proxy will be voted
in the manner directed above, but if no contrary direction is made, it will be
voted FOR Proposal 1 above and by the proxyholders, in the proxyholders'
discretion, as to any other matters properly transacted at the Special Meeting
or any adjournments or postponements thereof.

                               Dated:
                                      ------------------------------------ 


                               ------------------------------------------- 
                               Signature of Stockholder


                               ------------------------------------------- 
                               Printed Name of Stockholder


                               ------------------------------------------- 
                               Title (if appropriate)


                               Please sign exactly as name appears hereon.
                               If signing as attorney, executor,
                               administrator, trustee or guardian, please
                               give full title as such, and, if signing for
                               a corporation, please give your title. When
                               shares are in the names of more than one
                               person, each should sign.

                               CHECK HERE IF YOU PLAN TO ATTEND THE 
                               SPECIAL MEETING   [ ]