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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

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                                    FORM 8-K

                                 CURRENT REPORT

                     PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

        Date of Report (Date of earliest event reported): May 5, 1998


                                     0-27352
                            (Commission File Number)

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                                 HYBRIDON, INC.
             (Exact name of registrant as specified in its charter)

        Delaware                                            3072298
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  (State of Incorporation)                               (IRS Employer
                                                      Identification Number)

               620 Memorial Drive, Cambridge, Massachusetts 02139
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              (Address of registrant's principal executive office)

                                 (617) 528-7000
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                         (Registrant's telephone number)

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ITEM 5. OTHER EVENTS

         On May 6, 1998 Hybridon,  Inc. (the "Company") issued the press release
attached hereto as Exhibit 99.1.

ITEM 7. FINANCIAL STATEMENTS AND EXHIBITS


        Exhibit No.                       Title
        -----------                       -----

        99.1                       Press Release Dated May 6, 1998


ITEM 9. SALES OF EQUITY SECURITIES PURSUANT TO REGULATION S

        On May 5, 1998,  (the  "Closing  Date"),  the  Company  closed a private
placement (the "Offering") of approximately  3.2 million shares of common stock,
par value $.001 per share,  of the Company (the "Common  Stock"),  sold at $2.00
per share,  and warrants (the "Equity  Warrants") to purchase Common Stock,  for
aggregate gross proceeds of approximately  $6.3 miliion.  The securities sold in
the Offering (the "Offering  Securities")  were issued in offshore  transactions
pursuant to  Regulation  S  promulgated  under the  Securities  Act of 1933,  as
amended (the "Securities  Act"). The purchasers of the Offering  Securities were
"accredited  investors"  (as  defined  in  Regulation  D  promulgated  under the
Securities Act).

        The Equity Warrants are convertible  into the amount of shares of Common
Stock  equal to 25% of the  number of shares of Common  Stock  purchased  in the
Offering,  and are  exercisable  at $2.40 per  share for a period of five  years
commencing  on the Closing Date.  The Equity  Warrants are not subject to a call
provision.

        In addition,  on May 5, 1998, the Company closed a private  placement of
(i)  approximately  3.6 million  shares of Common Stock and warrants to purchase
Common  Stock and (ii)  approximately  114,300  shares  of Series A  Convertible
Preferred Stock, par value $.01 per share (the "Series A Preferred Stock"), sold
at $70 per share, and warrants to purchase Common Stock, to accredited investors
pursuant to Section 4(2) of the Securities  Act.  Furthermore,  by press release
dated May 6, 1998,  the  Company  announced  that  approximately  $48.6  million
principal  amount  of its 9%  Convertible  Subordinated  Notes due 2004 (the "9%
Notes") had been  tendered to the Company to be exchanged for shares of Series A
Preferred  Stock and warrants to purchase Common Stock pursuant to the Company's
exchange offer,  leaving only  approximately $1.4 million principal amount of 9%
Notes  outstanding.  Finally,  by press release  dated May 6, 1998,  the Company
announced  that  all  of  the  recent  purchasers  of its  Units  (the  "Units")
consisting  of 14%  Notes  due 2007 and  Common  Stock  warrants  had  agreed to
exchange such Units for Common Stock (priced at $2.00 per share) and warrants to
purchase Common Stock.




                                   SIGNATURES


         Pursuant to the  requirements  of the Securities  Exchange Act of 1934,
the  registrant  has duly  caused  this report to be signed on its behalf by the
undersigned, thereunto duly authorized.


                                 HYBRIDON, INC.

                                 By:   /s/ E. ANDREWS GRINSTEAD, III
                                       ---------------------------------
                                       Name:   E. Andrews Grinstead, III
                                       Title:  Chairman of the Board,
                                               President and Chief
                                               Executive Officer

                                 Date:  May 8, 1998