Exhibit 99.1

ARIAD Announces Proposed Public Offering of Common Stock

    CAMBRIDGE, Mass.--(BUSINESS WIRE)--March 15, 2004--ARIAD
Pharmaceuticals, Inc. (Nasdaq: ARIA) today announced that it has filed
a prospectus supplement with the Securities and Exchange Commission
related to an underwritten public offering of 6,000,000 shares of
common stock under an existing shelf registration statement. The
underwriters have been granted the option to purchase up to an
additional 900,000 shares to cover any over-allotments. All of the
shares are being sold by ARIAD.
    Lehman Brothers Inc. is acting as sole bookrunning manager in this
offering. Lazard Freres & Co., LLC, Adams, Harkness & Hill, Inc., JMP
Securities LLC and Rodman & Renshaw, LLC are acting as co-managers.
    This press release does not constitute an offer to sell or the
solicitation of an offer to buy any of the securities, nor shall there
be any sale of the securities in any state in which such offer,
solicitation or sale would be unlawful prior to registration or
qualification under the securities laws of any such state. A
prospectus supplement relating to these securities has been filed with
the Securities and Exchange Commission. This offering of the shares of
common stock may be made only by means of the prospectus supplement
and related prospectus, a copy of which is available from Lehman
Brothers, Inc., Prospectus Department, c/o ADP Financial Services,
Integrated Distribution Services, 1155 Long Island Avenue, Edgewood,
New York 11717; 631-254-7106.
    ARIAD is engaged in the discovery and development of breakthrough
medicines to treat cancer by regulating cell signaling with small
molecules.

    CONTACT: ARIAD Pharmaceuticals, Inc.
             Tom Pearson, 610-407-9260
             or
             Kathy Lawton, 617-621-2345