EXHIBIT 5.1

                                  May 19, 2003

ARIAD Pharmaceuticals, Inc.
26 Landsdowne Street
Cambridge, MA 02139-4234

Ladies and Gentlemen:

      We have acted as counsel to ARIAD Pharmaceuticals, Inc., a Delaware
corporation (the "Company"), in connection with the preparation and filing with
the Securities and Exchange Commission (the "Commission") of (i) a Registration
Statement on Form S-3, Registration No. 333-76486, as amended (the "Initial
Registration Statement"), and (ii) a second Registration Statement on Form S-3
to be filed pursuant to Rule 462(b) promulgated under the Securities Act of
1933, as amended (the "462(b) Registration Statement," and together with the
Initial Registration Statement, the "Registration Statement"). This opinion is
being rendered to you in connection with the filing of the 462(b) Registration
Statement, pursuant to which the Company is registering 627,712 of its shares
(the "Shares") of common stock, $.001 par value per share (the "Common Stock").
All capitalized terms used herein and not otherwise defined shall have the
respective meanings given to them in the Registration Statement.

      In connection with this opinion, we have examined the Company's
Certificate of Incorporation and Restated By-Laws, both as amended and currently
in effect; the minutes of all pertinent meetings of stockholders and directors
of the Company relating to the Registration Statement and the transactions
contemplated thereby; such other records of the corporate proceedings of the
Company and certificates of the Company's officers as we have deemed relevant;
and the Registration Statement and the exhibits thereto.

      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, and subject to the limitations set forth below,
we are of the opinion that the Shares, when issued and delivered by the Company
against payment therefore, will be duly and validly issued, fully paid and
non-assessable shares of the Common Stock.

      Our opinion is limited to the General Corporation Law of the State of
Delaware (including the applicable provisions of the Delaware Constitution and
the reported

judicial decisions interpreting the laws) and the federal laws of the United
States of America, 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. The foregoing opinion is rendered as of the date
hereof. We assume no obligation to update such opinion to reflect any facts or
circumstances which may hereafter come to our attention or changes in the law
which may hereafter occur.

      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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