[LOGO HYBRIDON]


FOR IMMEDIATE RELEASE
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Contacts:

Hybridon, Inc.                               Noonan Russo Presence Euro RSCG
617-679-5500, x5517                          212.845.4269
Robert G. Andersen                           Brian Ritchie (media and investors)
E-mail: randersen@hybridon.com


  HYBRIDON, INC. ANNOUNCES PLANNED RECOGNITION OF APPROXIMATELY $26 MILLION OF
               DEFERRED REVENUE AS REVENUE IN THIRD QUARTER 2002

CAMBRIDGE, MA, SEPTEMBER 30, 2002 - Hybridon, Inc. (OTC Bulletin Board: HYBN.OB)
announced today that it will recognize approximately $26 million of previously
deferred revenue as revenue in the third quarter of fiscal year 2002.

On August 14, 2002, Hybridon and Isis Pharmaceuticals, Inc. entered into an
amendment to their Collaboration and License Agreement dated May 24, 2001. As
part of the amendment, as previously reported, Hybridon and Isis agreed to
cancel the remaining tranche payments due to each other under the agreement.
Also, as part of the amendment, Hybridon and Isis agreed to more specifically
define and limit each party's future collaborative obligations under the
agreement.

As a result of this amendment, the Company has been able to better estimate the
nature of its obligation and related cost of compliance and has determined that
such amended obligation and cost will be inconsequential. In accordance with
SAB101 Hybridon will now recognize as revenue approximately $26 million of funds
received since May 24, 2001 from Isis under the original Collaboration and
License Agreement. Hybridon had previously deferred this revenue because the
original agreement obligated Hybridon to potentially engage in significant
future activities which could have material related costs.

Hybridon will record the approximately $26 million as revenue on the Company's
financial statements for the third quarter of fiscal year 2002. This will result
in a decrease in the amount of deferred revenue and a



corresponding increase in stockholders' equity on Hybridon's balance sheet as of
September 30, 2002. Since the cash related to the deferred revenue was received
in 2001, this change will not impact the amount of cash on Hybridon's financial
statements.

"This amendment and resulting change in accounting is a favorable development
for Hybridon," said Robert Andersen, Hybridon's Chief Financial Officer. "While
this will not impact our cash position, the increase in stockholders' equity
which results from recognizing this revenue will significantly strengthen our
balance sheet."

ABOUT HYBRIDON

Hybridon, Inc. is a leader in the discovery and development of novel
therapeutics and diagnostics, based on synthetic DNA. The company now has four
technology platforms: 1) Synthetic immunomodulatory oligonucleotide (IMOTM)
motifs that act to modulate responses of the immune system; 2) Antisense
technology which uses synthetic DNA to block the production of disease-causing
proteins at the cellular level; 3) Synthetic DNA drug candidates that enhance
the antitumor activity of certain marketed anticancer drugs, thereby increasing
their effectiveness; and 4) CycliconTM probes, novel synthetic DNA structures
for identifying gene function, which can be used for target validation and drug
discovery as well as for PCR-based gene amplification..

This press release contains forward-looking statements concerning Hybridon that
involve a number of risks and uncertainties. For this purpose, any statements
contained herein that are not statements of historical fact may be deemed to be
forward-looking statements. Without limiting the foregoing, the words,
"believes," "anticipates," "plans," "expects," "estimates," "intends," "should,"
"could," "will," "may," and similar expressions are intended to identify
forward- looking statements.

There are a number of important factors that could cause Hybridon's actual
results to differ materially from those indicated by such forward-looking
statements set forth under the caption "Risk Factors" in Hybridon's Quarterly
Report on Form 10-Q for the period ended June 30, 2002, which important factors
are incorporated herein by reference. These factors include risks as to whether
Hybridon will be able to enter into additional collaboration and licensing
arrangements on acceptable terms or at all; whether results obtained in
preclinical studies, , or clinical trials will be indicative of results obtained
in future preclinical studies or clinical trials; whether Hybridon's products
will receive approval from the US Food and Drug Administration or equivalent
foreign regulatory agencies; whether, if such products receive



approval, they will be successfully distributed and marketed; and whether
Hybridon's cash resources will be sufficient to fund product development.

These forward-looking statements should not be relied upon as representing
Hybridon's views as of any date subsequent to the date of this release and
Hybridon disclaims any obligation to update these forward-looking statements.

This and other Hybridon press releases can be found at http://www.hybridon.com
and http://www.nrp-euro.com.

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