Exhibit 99.1

IMMUNOGEN APPOINTS NEW CHIEF FINANCIAL OFFICER

    CAMBRIDGE, Mass., March 5 /PRNewswire/ -- ImmunoGen, Inc. (Nasdaq: IMGN)
today announced the appointment of Gregg D. Beloff as Vice President and Chief
Financial Officer.  Mr. Beloff was most recently a Vice President in the
Healthcare Investment Banking Group of Adams, Harkness & Hill, where he
specialized in financial and advisory transactions for biotechnology and
healthcare companies.

    "We are delighted to welcome Gregg to the executive management team at
ImmunoGen," said Mitchel Sayare, Ph.D., Chairman and CEO of ImmunoGen, Inc.
"Gregg's considerable experience with the biotechnology industry as well as his
broad financial and business credentials will make him a valuable contributor to
our future success."

    Prior to joining Adams, Harkness & Hill, Mr. Beloff was a corporate
attorney with the law firm of Gaffin & Krattenmaker.  He is a member of both
the Massachusetts and Pennsylvania Bar Associations.  Mr. Beloff received his
Master of Business Administration from Carnegie Mellon University and his
Juris Doctorate from University of Pittsburgh School of Law.

    ImmunoGen, Inc. develops innovative biopharmaceuticals, primarily for cancer
treatment. The Company has created potent tumor-activated prodrugs, consisting
of drugs coupled to monoclonal antibodies for delivery to and destruction of
cancer cells. Its lead product, huC242-DM1/SB-408075 is in two Phase I/II
clinical trials for colorectal, pancreatic and certain non-small-cell lung
cancers. The Company has collaborative arrangements with GlaxoSmithKline,
Genentech, British Biotech, Abgenix, MorphoSys, and Avalon.

    THIS PRESS RELEASE INCLUDES FORWARD-LOOKING STATEMENTS BASED ON MANAGEMENT'S
CURRENT EXPECTATIONS. FACTORS THAT COULD CAUSE FUTURE RESULTS TO DIFFER
MATERIALLY FROM SUCH EXPECTATIONS INCLUDE, BUT ARE NOT LIMITED TO: THE ABILITY
TO SECURE FUTURE FUNDING; THE SUCCESS OF THE COMPANY'S RESEARCH STRATEGY; THE
APPLICABILITY OF THE DISCOVERIES MADE THEREIN; THE DIFFICULTIES INHERENT IN THE
DEVELOPMENT OF PHARMACEUTICALS, INCLUDING UNCERTAINTIES AS TO THE TIMING AND
RESULTS OF PRECLINICAL STUDIES; DELAYED ACHIEVEMENTS OF MILESTONES; RELIANCE ON
COLLABORATORS; UNCERTAINTY AS TO WHETHER THE COMPANY'S POTENTIAL PRODUCTS WILL
SUCCEED IN ENTERING HUMAN CLINICAL TRIALS AND UNCERTAINTY AS TO THE RESULTS OF
SUCH TRIALS; UNCERTAINTY AS TO WHETHER ADEQUATE REIMBURSEMENT FOR THESE PRODUCTS
WILL EXIST FROM THE GOVERNMENT, PRIVATE HEALTHCARE INSURERS AND THIRD-PARTY
PAYORS; AND THE UNCERTAINTIES AS TO THE EXTENT OF FUTURE GOVERNMENT REGULATION
OF THE PHARMACEUTICAL BUSINESS.

     Contact:
     Mitchel Sayare, Ph.D.
     Chairman and CEO
     ImmunoGen, Inc.
     (617) 995-2500
     http://www.immunogen.com