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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): April 21, 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 9. SALES OF EQUITY SECURITIES PURSUANT TO REGULATION S

        On April 21,  1998,  as part of a private  placement  (the  "Offering"),
Hybridon,  Inc. (the "Company")  sold $300,000 in principal  amount of Notes due
2007 (the "Offering  Notes"),  and warrants (the  "Warrants") to purchase common
stock,  par value $.001 per share, of the Company,  pursuant to the terms of the
Offering  described  in its Current  Report on Form 8-K,  and the press  release
filed as an exhibit  thereto,  dated  January  22, 1998 (the  "January  22, 1998
8-K").  The  Offering  Notes were issued at face value in offshore  transactions
pursuant to  Regulation  S  promulgated  under the  Securities  Act of 1933,  as
amended (the  "Securities  Act").  The  purchasers  of the  Offering  Notes were
accredited   investors  (as  defined  in  Regulation  D  promulgated  under  the
Securities Act).

        The  terms of  conversion  of the  Offering  Notes  and the terms of the
Warrants are described in the January 22, 1998 8-K.

        The net proceeds to the Company from the Offering are presently intended
to be used for  general  corporate  purposes,  primarily  research  and  product
development  activities,  including costs of preparing  Investigational New Drug
applications and conducting preclinical studies and clinical trials, the payment
of payroll and other  accounts  payable and for debt service  required under the
Company's debt obligations.




                                   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: April 27, 1998