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

                                   FORM 12b-25

                           NOTIFICATION OF LATE FILING

(Check One):   |X| Form 10-K  |_| Form 20-F  |_| Form 11-K  |_| Form 10-Q  
               |_| Form N-SAR

               For Period Ended: December 31, 1998 

               [ ] Transition  Report on Form 10-K 
               [ ] Transition Report on Form 20-F 
               [ ] Transition  Report on Form 11-K 
               [ ] Transition Report on Form 10-Q 
               [ ] Transition Report on Form N-SAR
               For the Transition Period Ended:_________________________________

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  Read Instruction (on back page) Before Preparing Form. Please Print or Type.
Nothing  in this  form  shall be  construed  to imply  that the  Commission  has
verified any information contained herein.
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If the notification  relates to a portion of the filing checked above,  identify
the Item(s) to which the notification relates:
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PART I - REGISTRANT INFORMATION

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Full Name of Registrant:      Hybridon, Inc.
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Former Name if Applicable:    N/A
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Address of Principal Executive Office (Street and Number)

                      155 Fortune Blvd.
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City, State and Zip Code
                      Milford, Massachusetts  01757
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PART II -- RULES 12b-25(b) AND (c)

If the subject  report could not be filed without  reasonable  effort or expense
and the  registrant  seeks  relief  pursuant to Rule 12b- 25(b),  the  following
should be completed. (Check box if appropriate)


      [X] (a)  The reasons  described in  reasonable  detail in Part III of this
               form  could  not be  eliminated  without  unreasonable  effort or
               expense;
      [X] (b)  The subject annual report,  semi-annual report, transition report
               on Form 10-K, Form 20-F, 11-K or Form N-SAR, or portion  thereof,
               will be filed on or before the  fifteenth  calendar day following
               the  prescribed  due date;  or the  subject  quarterly  report of
               transition  report on Form 10-Q, or portion thereof will be filed
               on or before the fifth  calendar day following the prescribed due
               date; and
      [ ] (c)  The  accountant's  statement  or other  exhibit  required by Rule
               12b-25(c) has been attached if applicable.






PART III -- NARRATIVE State below in reasonable detail the reasons why Forms 10-K, 11-K, 10-Q, N-SAR, or the transition report or portion thereof, could not be filed within the prescribed time period. (Attach extra sheets if needed). The Registrant's Annual Report on Form 10-K for the fiscal year ended December 31, 1998 could not be filed within the prescribed time period because certain information relating to and necessary for the completion of the Registrant's financial statements and management's discussion and analysis of financial condition and results of operations could not be obtained by the Registrant within such time period without unreasonable effort or expense. Registrant believes that the subject Annual Report on 10-K will be filed within the prescribed grace period provided for under Rule 12b-25 promulgated by the Securities and Exchange Commission under the Securities Exchange Act of 1934, as amended. PART IV -- OTHER INFORMATION (1) Name and telephone number of person to contact in regard to this notification Monica C. Lord (212) 715-9348 --------------------- ----------------------- --------------------- (Name) (Area Code) (Telephone Number) (2) Have all other period reports required under Section 13 or 15(d) of the Securities Exchange Act of 1934 or Section 30 of the Investment Company Act of 1940 during the preceding 12 months (or for such shorter) period that the registrant was required to file such reports) been filed? If answer is no, identify report(s). |X| Yes |_| No - -------------------------------------------------------------------------------- (3) Is it anticipated that any significant change in results of operations from the corresponding period for the last fiscal year will be reflected by the earnings statements to be included in the subject report or portion thereof? |X| Yes |_| No If so, attach an explanation of the anticipated change, both narratively and quantitatively, and, if appropriate, state the reasons why a reasonable estimate of the results cannot be made. See Attachment I - -------------------------------------------------------------------------------- Hybridon, Inc. - -------------------------------------------------------------------------------- (Name of Registrant as Specified in Charter) has caused this notification to be signed on its behalf by the undersigned hereunto duly authorized. Date 04/01/99 By /s/ E. Andrews Grinstead, III ---------------- -------------------------------------------- E. Andrews Grinstead, III Chairmen, President and Chief Executive Officer INSTRUCTION: The form may be signed by an executive officer of the registrant or by any other duly authorized representative. The name and title of the person signing the form shall be typed or printed beneath the signature. If the statement is signed on behalf of the registrant by an authorized representative (other than an executive officer), evidence of the representative's authority to sign on behalf of the registrant shall be filed with the form. ATTENTION - -------------------------------------------------------------------------------- Intentional misstatements or omissions of fact constitute Federal Criminal Violations (See 18 U.S.C. 1001). - --------------------------------------------------------------------------------

Attachment I The Registrant estimates that its loss from operations for the twelve months ended December 31, 1998, will be approximately $ 26,000,000 as compared with loss from operations of $ 69,461,326 during the twelve months ended December 31, 1997. The Registrant estimates that its net loss for the twelve months ended December 31, 1998, will be approximately $ 17,000,000 as compared with a net loss of $ 69,461,326 during the twelve months ended December 31, 1997. These decreases resulted primarily from implementation of the Company's restructuring plan which was commenced in the second half of 1997.