<PAGE> 1
Filed Pursuant to Rule 424(b)(3)
REGISTRATION NO. 333-31795
PROSPECTUS SUPPLEMENT NO. 2 DATED OCTOBER 26, 1999 TO THE
PROSPECTUS DATED JULY 22, 1997, AS AMENDED BY
PROSPECTUS SUPPLEMENT NO. 1 DATED MAY 20, 1999, OF
IMMUNOGEN, INC.
This Prospectus Supplement No. 2 amends the information in the table under
the caption "Selling Stockholders" in the Prospectus dated July 22, 1997, as
amended by Prospectus Supplement No. 1 dated May 20, 1999, by deleting the
information as to Southbrook International Investments Ltd. as a Selling
Stockholder with respect to 1,690,360 shares of ImmunoGen, Inc. Common Stock,
$.01 par value per share, and substituting therefor the following information:
<TABLE>
<CAPTION>
Shares Owned Number of Shares Owned
Prior to Shares Being After Offering
Selling Stockholder Offering Offered Number Percent
------------------- ------------ ------------ ------ -------
<S> <C> <C> <C> <C>
Strong River
Investments, Inc. 1,591,039 1,591,039 0 0
Trippoak Advisors, Inc. 99,321 99,321 0 0
</TABLE>
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This Prospectus Supplement No. 2 should be read in conjunction with the
Prospectus dated July 22, 1997, as amended by Prospectus Supplement No. 1 to the
Prospectus dated May 20, 1999.
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