EXHIBIT 5.1


                  [Brobeck, Phleger & Harrison LLP Letterhead]

                                 August 8, 2000

Ligand Pharmaceuticals Incorporated
10275 Science Center Drive
San Diego, California  92121

          Re:  LIGAND PHARMACEUTICALS INCORPORATED REGISTRATION STATEMENT ON
               FORM S-8 FOR (I) 500,000 SHARES OF COMMON STOCK ISSUABLE UNDER
               THE 1992 STOCK OPTION/STOCK ISSUANCE PLAN, AS AMENDED, AND (II)
               50,000 SHARES OF COMMON STOCK ISSUABLE UNDER THE EMPLOYEE STOCK
               PURCHASE PLAN, AS AMENDED.

Ladies and Gentlemen:

          We have acted as counsel to Ligand Pharmaceuticals Incorporated (the
"Company") in connection with the registration on Form S-8 (the "Registration
Statement") under the Securities Act of 1933, as amended, of (i) an additional
500,000 shares of the Company's common stock (the "Common Stock") for issuance
under the Company's 1992 Stock Option/Stock Issuance Plan, as amended (the
"Stock Plan"), and (ii) an additional 50,000 shares of Common Stock under the
Company's Employee Stock Purchase Plan, as amended (the "Employee Plan"). All of
such shares of Common Stock are collectively referred to herein as the "Shares."

          This opinion is being furnished in accordance with the requirements of
Item 8 of Form S-8 and Item 601(b)(5)(i) of Regulation S-K.

          We have reviewed the Company's charter documents and the corporate
proceedings taken by the Company in connection with the establishment and
amendment of the Stock Plan and the Employee Plan. Based on such review, we are
of the opinion that if, as and when the additional 550,000 Shares reserved in
the aggregate under the Stock Plan and the Employee Plan have been issued and
sold (and the consideration therefor received) pursuant to (a) the provisions of
option agreements duly authorized under the Stock Plan and in accordance with
the Registration Statement, or (b) duly authorized direct stock issuances in
accordance with the Stock Plan and the Employee Plan and in accordance with the
Registration Statement, those Shares will be legally issued, fully paid and
nonassessable.

          We consent to the filing of this opinion letter as Exhibit 5.1 to the
Registration Statement. In giving this consent, we do not thereby admit that we
are within the category of persons whose consent is required under Section 7 of
the Securities Act of 1933, as amended, or the rules and regulations of the
Securities and Exchange Commission promulgated thereunder, or Item 509 of
Regulation S-K.

          This opinion letter is rendered as of the date first written above and
we disclaim any obligation to advise you of facts, circumstances, events or
developments which hereafter may be brought to our attention and which may
alter, affect or modify the opinion expressed herein. Our opinion is expressly
limited to the matters set forth above and we render no opinion, whether by
implication or otherwise, as to any other matters relating to the Company, the
Stock Plan, the Employee Plan or the Shares.

                                 Very truly yours,


                                 BROBECK, PHLEGER & HARRISON LLP