Exhibit 16




October 5, 2001



Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549

Commissioners:

We have read the statements made by ImmunoGen, Inc. (copy attached), which we
understand will be filed with the Commission pursuant to Item 4 of Form
8-K/A, as part of the Company's Form 8-K/A report dated August 31, 2001,
filed October 5, 2001. We agree with the statements concerning our Firm in
such Form 8-K/A.

/s/ PricewaterhouseCoopers LLP