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                                                                       EXHIBIT 5

November 2, 1999

Ladies and Gentlemen:

I am Senior Vice President, General Counsel and Secretary of Genentech, Inc.
(the "Company"). In connection with this opinion, I have examined the following
documents:

     o    the Company's Post-Effective Amendment No. 1 Registration Statement on
          Form S-8, registration number 333-83989 (the "Registration Statement")
          to be filed with the Securities and Exchange Commission covering the
          offering of 7,500,000 shares of the Company's Common Stock, par value
          $.02 per share (the "Shares"), pursuant to the Company's 1999 Stock
          Plan and 1991 Employee Stock Plan (the "Plans") and the related
          Prospectuses;

     o    the Company's Amended and Restated Certificate of Incorporation and
          Bylaws; and

     o    such other documents, records, certificates, memoranda and other
          instruments as I deem necessary as a basis for this opinion.

I have assumed the genuineness and authenticity of all documents submitted to me
as originals, the conformity to originals of all documents submitted to me as
copies thereof, and the due execution and delivery of all documents where due
execution and delivery are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, I am of the opinion that
the Shares, when sold and issued in accordance with the Registration Statement
and either of the Plans and the related Prospectus, will be validly issued,
fully paid, and nonassessable (except as to shares issued pursuant to certain
deferred payment arrangements, which will be fully paid and nonassessable when
such deferred payments are made in full).

I am admitted to practice only in the State of California. The opinions set
forth herein are limited to matters of the General Corporation Law of the state
of Delaware and the federal securities laws of the United States.

I consent to the filing of this opinion as an exhibit to the Registration
Statement.

                                                   Very truly yours,



                                                   /s/ STEPHEN G. JUELSGAARD
                                                   -----------------------------
                                                   Stephen G. Juelsgaard
                                                   Senior Vice President,
                                                   General Counsel and Secretary