1 Exhibit 99.1 [LOGO:HYBRIDON] [LOGO:NEWS RELEASE] FOR IMMEDIATE RELEASE Hybridon, Inc. TEL: 617.528.7000 Fax: 617.528.7001 620 Memorial Drive www.hybridon.com Cambridge, MA 02139 Contact: Robin Hogen Vice President, Corporate Communications and Public Affairs 617.528.7504 HYBRIDON ENTERS INTO AGREEMENT FOR THE SALE OF $50 MILLION OF CONVERTIBLE SUBORDINATED NOTES CAMBRIDGE, MA., March 27, 1997 - Hybridon, Inc. (Nasdaq: HYBN), announced today that it has entered into an agreement for the sale of 9% convertible subordinated notes due 2004 in the original purchase amount of $50,000,000. The closing is expected to occur on April 2, 1997, and is subject to the satisfaction of certain conditions. The notes will be convertible into shares of common stock at a price of $ 7.0125 per share. Hybridon, a biopharmaceutical company headquartered in Cambridge, Massachusetts, is a leader in the discovery and development of novel genetic medicines based primarily on antisense technology. Antisense involves the use of synthetic segments of nucleic acid, called oligonucleotides, constructed through rational drug design to modulate protein expression by interacting at the genetic level with target messenger RNA. ### NOTE: THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. ACCORDINGLY, SUBJECT TO REGISTRATION OR CERTAIN EXEMPTIONS THEREFROM, THESE SECURITIES MAY NOT BE OFFERED OR SOLD DIRECTLY OR INDIRECTLY IN THE UNITED STATES OF AMERICA, ITS TERRITORIES OR POSSESSIONS. Leadership in Genetic Antisense Medicine