EXHIBIT 5.1

                                 October 3, 2003

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

Ladies and Gentlemen:

         This opinion is furnished to you in connection with the filing by ARIAD
Pharmaceuticals, Inc., a Delaware corporation (the "Company"), with the
Securities and Exchange Commission (the "Commission") under the Securities Act
of 1933, as amended (the "Securities Act"), of a Prospectus Supplement dated
October 3, 2003 (the Prospectus Supplement") to a Registration Statement on Form
S-3 (File No. 333-106788) as declared effective by the Commission on July 16,
2003 (the "Registration Statement") with respect to 6,438,114 shares (the
"Shares") of its common stock, $0.001 par value per share (the "Common Stock").
The Shares are to be sold to a group of investors pursuant to a Placement Agency
Agreement by and among the Company and Lehman Brothers Inc. and Rodman &
Renshaw, Inc., as placement agents, dated as of October 3, 2003 (the "Placement
Agency Agreement"), as well as pursuant to stock purchase agreements by and
between the Company and each of the investors. Such Placement Agency Agreement
and the form of stock purchase agreement will be filed as exhibits to a Current
Report on Form 8-K (the "8-K"). The Shares are being sold by the Company.

         In connection with this opinion, we have examined the Company's
Certificate of Incorporation, as amended, and Restated Bylaws, as amended; the
minutes of all pertinent meetings of stockholders and directors of the Company
relating to the Registration Statement, the Prospectus Supplement and the
transactions contemplated thereby; such other records of the corporate
proceedings of the Company and certificates of the Company's officers as we
deemed relevant for the purposes of rendering the opinions in this letter; the
Placement Agency Agreement and the form of stock purchase agreement; the
Registration Statement (including the exhibits thereto filed with the
Commission) and the related prospectus (including the documents incorporated by
reference thereto); and the Prospectus Supplement.

         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, photostatic or facsimile 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 by the Company and
delivered by the Company against payment therefor as contemplated by the
Placement Agency Agreement and stock Purchase agreements, will be duly and
validly issued, fully paid and non-assessable shares of the Common Stock.



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         Our opinion is limited to the General Corporation Laws of the State of
Delaware (including the applicable provisions of the Delaware Constitution and
the reported judicial decisions interpreting such laws) and the United States
Federal Laws, 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. To the extent that any applicable document is stated to be
governed by the laws of another jurisdiction, we have assumed for purposes of
this opinion that the laws of such jurisdiction are identical to the state laws
of the State of Delaware.

         Please note that we are opining only as to the matters expressly set
forth herein, and no opinion should be inferred as to any other matters. This
opinion is based upon currently existing statutes, rules, regulations and
judicial decisions, and we disclaim any obligation to advise you of any change
in any of these sources of law or subsequent legal or factual developments which
might affect any matters or opinions set forth herein.

         We hereby consent to the filing of this opinion with the Commission as
an exhibit to the 8-K and the Registration Statement in accordance with the
requirements of Item 601(b)(5) of Regulation S-K under the Securities Act and to
the use of this Firm's name therein and in the Prospectus Supplement under the
caption "Legal Matters." In giving such consent, we do not hereby admit that we
are in the category of persons whose consent is required under Section 7 of the
Securities Act or the rules and regulations of the Commission.

                         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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