1
                                                                     EXHIBIT 5.1



                  [KUMMER KAEMPFER BONNER & RENSHAW LETTERHEAD]



                                                             September 12, 2000



Watson Pharmaceuticals, Inc.
311 Bonnie Circle
Corona, CA 92880

Ladies and Gentleman:

                  We have acted as counsel for Watson Pharmaceuticals, Inc., a
Nevada corporation (the "Company"), in connection with the registration
statement on Form S-8 ("Registration Statement") to be filed by the Company with
the Securities and Exchange Commission covering the offer and sale of up to
832,500 shares of the Company's common stock, $0.0033 par value per share
("Common Stock"), to be issued in connection with the Schein Pharmaceutical,
Inc. 1995 Non-Employee Director Stock Option Plan, Schein Pharmaceutical, Inc.
1999 Stock Option Plan, The Retirement Plan of Schein Pharmaceutical, Inc. and
Affiliates, and the Danbury Pharmaceutical Puerto Rico, Inc. Banco Popular de
Puerto Rico Master Defined Contribution Retirement Plan.

                  In rendering this opinion, we have examined and relied on the
following documents: (i) the Company's Articles of Incorporation, as amended,
and Bylaws, as amended, (ii) the resolutions adopted by the Board of Directors
of the Company on May 23, 2000, (iii) the Registration Statement, and (iv) such
other documents, legal opinions and precedents, corporate and other records of
the Company, and certificates of public officials and officers of the Company
that we have deemed necessary or appropriate to provide a basis for the opinion.

                  Based upon and subject to the foregoing, in our opinion, the
shares of Common Stock of the Company which are being offered and sold by the
Company pursuant to the Registration Statement, when sold in the manner and for
the consideration contemplated by the Registration Statement, will be legally
issued, fully paid and non-assessable.

                  We consent to the filing of this opinion as an Exhibit to the
Registration Statement and to the reference to our firm under the heading "Legal
Matters."



                                       Very truly yours,

                                       /s/ Kummer Kaempfer Bonner & Renshaw