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                                                                 EXHIBIT 5.1



                                 December 29, 1997



Collagen Corporation
2500 Faber Place
Palo Alto, CA  94303

        REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

        We have examined the Registration Statement on Form S-8 (the
"Registration Statement") to be filed by you with the Securities and Exchange
Commission (the "Commission") on or about December 29, 1997 in connection with
the registration under the Securities Act of 1933, as amended, of an aggregate
of 100,000 shares of your Common Stock (the "Shares") reserved for issuance
under the 1985 Employee Stock Purchase Plan. As your counsel in connection with
this transaction, we have examined the proceedings taken and are familiar with
the proceedings proposed to be taken by you in connection with the sale and
issuance of the Shares.

        It is our opinion that upon conclusion of the proceedings being taken or
contemplated by us, as your counsel, to be taken prior to the issuance of the
Shares, and upon completion of the proceedings being taken in order to permit
such transactions to be carried out in accordance with the securities laws of
the various states where required, the Shares when issued and sold in the manner
described in the Registration Statement will be legally and validly issued,
fully paid and non-assessable.

        We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement and in any amendments thereto.

                                    Sincerely,

                                    VENTURE LAW GROUP,
                                    A Professional Corporation