POWER OF ATTORNEY

KNOW ALL BY THESE PRESENT, that the undersigned hereby constitutes
and appoints each of Virginia Lavery of ImmunoGen, Inc.
(the "Company") and Jonathan L. Kravetz and Megan Gates of
Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., signing
singly,
with full power of substitution, the undersigned's true and
lawful attorney-in-fact to:

(1) Execute for and on behalf of the undersigned, in the
undersigned's capacity as an officer, director and/or 10%
shareholder of the Company, Forms 3, 4 and 5 in accordance
with
Section 16(a) of the Securities Exchange Act of 1934 and the
rules thereunder;

(2) Do and perform any and all acts for and on behalf of
the undersigned which may be necessary or desirable to
complete and
execute any such Form 3, 4 or 5 and timely file such form
with
the United States Securities and Exchange Commission and
any stock
exchange or similar authority; and

(3) Take any other action of any type whatsoever in connection
with
the foregoing which, in the opinion of such attorney-in-fact,
may
be of benefit to, in the best interest of, or legally required
by,
the undersigned, it being understood that the documents executed
by such attorney-in-fact on behalf of the undersigned pursuant
to this Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney-in-fact
may approve in such attorney-in-fact's discretion.

The undersigned hereby grants to each such attorney-in-fact
full
power and authority to do and perform any and every act and
thing whatsoever requisite, necessary, or proper to be done
in the
exercise of the rights and powers herein granted, as fully
to all intents and purposes as the undersigned might or
could do if
personally present, with full power of substitution or
revocation, hereby ratifying and confirming all that such attorney-in-fact, or
such attorney-in-fact's substitute or substitutes, shall
lawfully
do or cause to be done by virtue of this Power of Attorney
and the rights and powers herein granted.  The undersigned
acknowledges that the foregoing attorneys-in-fact, in serving
in such capacity at the request of the undersigned, are not
assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Securities
Exchange Act of 1934.

This Power of Attorney shall remain in full force and effect
until
the undersigned is no longer required to file Forms 3, 4 and
5 with respect to the undersigned's holdings of and
transactions in
securities issued by the Company, unless earlier revoked
by the undersigned in a signed writing delivered to the
foregoing attorneys-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed this 21st day of June 2004.



/s/ Joseph J. Villafranca
								____________________________________________

Print Name: Joseph J. Villafranca