<PAGE> 1
Filed Pursuant to Rule 424(b)(3)
REGISTRATION NO. 333-31795
PROSPECTUS SUPPLEMENT NO. 1 DATED MAY 20, 1999 TO THE
PROSPECTUS DATED JULY 22, 1997 OF
IMMUNOGEN, INC.
This Prospectus Supplement No. 1 amends the information in the table under
the caption "Selling Stockholders" in the Prospectus dated July 22, 1997 by
deleting the information as to Brown Simpson, LLC as a Selling Stockholder with
respect to 286,939 shares of ImmunoGen, Inc. Common Stock, $.01 par value per
share, and substituting therefore the following information:
<TABLE>
<CAPTION>
Shares Owned Number of Shares Shares Owned After
Selling Stockholder Prior to Offering Being Offered Offering
- ------------------- ----------------- ------------- ------------------
Number Percent
------ -------
<S> <C> <C> <C> <C>
Brown Simpson ORD 286,939 286,939 0 *
Investments, LLC
</TABLE>
--------------------------------
This Prospectus Supplement No. 1 should be read in conjunction with the
Prospectus dated July 22, 1997.
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