Alnylam Pharmaceuticals this week announced that it would offer for sale 8.625 million of its shares at $10.75 per share.
The company's shares have been trading around $12.50 this week.
Alnylam is offering 7.5 million shares to the public, and the underwriters of the offering have exercised an option to purchase 1.125 million additional shares.
The transaction, which would pull in $86.9 million for the company, is expected to close on Feb. 21.