1

                                                                    Exhibit 99.1

                             [HYBRIDON LETTERHEAD]


                                  NEWS RELEASE


FOR IMMEDIATE RELEASE


                      HYBRIDON ANNOUNCES PRIVATE FINANCING


CAMBRIDGE, MA., November 18, 1997 - Hybridon, Inc. (Nasdaq: HYBN) today
announced that it plans to commence a private offering (the "Private Offering")
of shares of its Common Stock pursuant to which it intends to sell at one or
more closings an aggregate of up to $50.0 million of its Common Stock (with a
minimum first closing of at least $12.5 million). The Company expects to use
the proceeds of the Private Offering for general corporate purposes, including
primarily costs of preparing investigational new drug applications and
conducting preclinical studies and clinical trials. The Company anticipates
that approximately 50% of the proceeds of the Private Offering will be
generated from the sale of Common Stock to U.S. investors and approximately 50%
of the proceeds of the Private Offering will be generated from the sale of
Common Stock to overseas investors. The Company anticipates that a significant
portion of the proceeds will be generated from existing investors.

It is currently contemplated that the Common Stock to be issued and sold in the
Private Offering will be offered and sold at all closings at an effective price
per share equal to the lowest of (i) $1.25 per share, (ii) 85% of the average
closing bid price of the Company's Common Stock at the time the Private
Offering is commenced, (iii) the average closing bid price of the Company's
Common Stock for the 30 consecutive trading days immediately preceding any
closing and (iv) the average closing bid price of the Company's Common Stock
for the five consecutive trading days immediately preceding any closing.
Purchasers of the Common Stock sold in the Private Offering will also be
entitled and subject to certain contractual rights, preferences and limitations.

THE SHARES OF COMMON STOCK OFFERED IN THE PRIVATE OFFERING HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE OFFERED
OR SOLD IN THE U.S. ABSENT REGISTRATION OR AN APPLICABLE EXEMPTION FROM
REGISTRATION REQUIREMENTS.

Hybridon, headquartered in Cambridge, Massachusetts, is a leader in the
discovery and development of novel genetic medicines for the treatment of
important diseases, based primarily on antisense technology. Antisense
technology involves the use of synthetic segments of DNA and RNA to stop the
production of disease-associated proteins by interacting at the genetic level
with target strands of messenger RNA.

                                      ###

This press release contains forward-looking statements that involve a number of
risks and uncertainties. There can be no assurance that the Company will
receive gross proceeds from the Private Offering of at least $12.5 million or
as to when or if the Company will ever consummate the Private Offering. There
can also be no assurance that the terms of the Private Offering will not
change from those described above or that the relative proceeds generated from
the sale of Common Stock to U.S. investors and overseas investors will be as
anticipated by the Company.



                    Leadership in Genetic Antisense Medicine