Exhibit 5.1


                                  October 7, 1996

Biogen, Inc.
14 Cambridge Center
Cambridge, Massachusetts 02142

Gentlemen:

    We have acted as counsel to Biogen, Inc., a Massachusetts
corporation (the "Company"), in connection with the preparation and
filing with the Securities and Exchange Commission (the
"Commission") of a Registration Statement on Form S-8 (the
"Registration Statement"), pursuant to which the Company is
registering under the Securities Act of 1933, as amended, a total
of 908,400 previously issued shares (the "Shares") of its common
stock, $.01 par value per share (the "Common Stock").  The Shares
are to be sold by certain shareholders of the Company (the "Selling
Shareholders").  The Company has not engaged any underwriters in
connection with the proposed filing of the Registration Statement. 
This opinion is being rendered in connection with the filing of the
Registration Statement.

    In connection with this opinion, we have examined the
Company's Articles of Organization and By-Laws, as amended to date;
such records of the corporate proceedings of the Company as we
deemed material; and the Registration Statement and the exhibits
thereto filed with the Commission.

    In our examination, we have assumed the genuineness of all
signatures, the legal capacity of natural persons, the authenticity
of all documents submitted to us as originals, the conformity to
original documents of all documents submitted to us as certified or
photostatic copies and the authenticity of the originals of such
copies.

    Based upon the foregoing, we are of the opinion that, (i) the
Shares have been duly and validly authorized by the Company, and
(ii) the Shares are duly and validly issued, fully paid and
non-assessable shares of the Common Stock, free of preemptive
rights.

    Our opinion is limited to the General Corporation Law of the
Commonwealth of Massachusetts, and we express no opinion with
respect to the laws of any other jurisdiction.  No opinion is
expressed herein with respect to the qualification of the Shares
under the securities or blue sky laws of any state or any foreign
jurisdiction.

    We understand that you wish to file this opinion as an exhibit
to the Registration Statement, and we hereby consent thereto.  We
hereby further consent to the reference to us under the caption
"Legal Matters" in the prospectus included in the Registration
Statement.

                             Very truly yours,

                             /s/ Mintz, Levin, Cohn, Ferris, 
                                  Glovsky and Popeo, P.C.

                             Mintz, Levin, Cohn, Ferris,
                                  Glovsky and Popeo, P.C.








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