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                                                                     EXHIBIT 5.1



                                VENTURE LAW GROUP
                            a Professional Corporation
                               2800 Sand Hill Road
                              Menlo Park, CA 94025


                                  May 14, 1997


Celtrix Pharmaceuticals, Inc.
3055 Patrick Henry Drive
Santa Clara, California 95054

         REGISTRATION STATEMENT ON FORM S-3

Ladies and Gentlemen:

         We have examined the Registration Statement on Form S-3 to be filed by
you with the Securities and Exchange Commission on or about May 15, 1997 (the
"Registration Statement") in connection with the registration under the
Securities Act of 1933, as amended, of a total of 8,582,810 shares of your
Common Stock (the "Shares"), 5,721,876 of which Shares were issued to several
institutional stockholders (the "Stockholders") in a private placement on April
1, 1997, and 2,860,934 of which Shares are issuable upon the exercise of
warrants (the "Warrants") issued to such Stockholders in such private placement.
As your legal counsel, we have examined the proceedings taken in connection with
the sale of the Shares and the Warrants to the Stockholders and are familiar
with the proceedings proposed to be taken by you, and the Stockholders in
connection with the sale of the Shares under the Registration Statement.

         It is our opinion that the Shares are legally and validly issued, fully
paid and nonassessable (or in the case of the Shares issuable upon exercise of
the Warrants, will be legally and validly issued, fully paid and nonassessable
upon exercise of the Warrants in accordance with their terms) and when resold in
the manner referred to in the Registration Statement, the Shares will be legally
and validly issued, fully paid and nonassessable.

         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 it appears in the
Registration Statement and any amendments to it.



                                       Sincerely,


                                       VENTURE LAW GROUP
                                       A Professional Corporation

                                       /s/ Venture Law Group

CWJ