THE TERMS OF THE NOTES ISSUABLE UPON EXERCISE HEREOF ARE SUBJECT TO THE TERMS OF
A SUBSCRIPTION  AGREEMENT AND AN  INTERCREDITOR  AGREEMENT,  COPIES OF WHICH ARE
AVAILABLE FROM HYBRIDON, INC. (THE "COMPANY").  NEITHER THESE SECURITIES NOR THE
NOTES  ISSUABLE  UPON  EXERCISE  HEREOF  NOR  THE  COMMON  STOCK  ISSUABLE  UPON
CONVERSION  THEREOF HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 OR ANY
APPLICABLE  STATE  SECURITIES  LAWS.  THEY MAY NOT BE SOLD,  OFFERED  FOR  SALE,
PLEDGED  OR  HYPOTHECATED   OR  OTHERWISE   TRANSFERRED  IN  THE  ABSENCE  OF  A
REGISTRATION  STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES  UNDER SUCH ACT
OR AN EXEMPTION  THEREFROM.  ANY SUCH TRANSFER MAY ALSO BE SUBJECT TO APPLICABLE
STATE SECURITIES LAWS.

THE  SECURED  PARTY (AS  DEFINED  IN THE  SUBSCRIPTION  AGREEMENT)  SHALL BE THE
EXCLUSIVE  AGENT OF THE HOLDER OF THE NOTES  ISSUABLE UPON EXERCISE  HEREOF WITH
RESPECT  TO  CERTAIN  ACTIONS  UNDER  SUCH  NOTES  AND  UNDER  THE  SUBSCRIPTION
AGREEMENT; THE SECURED PARTY, IN ITS SOLE DISCRETION,  MAY TAKE OR FOREBEAR FROM
TAKING CERTAIN ACTIONS UNDER THE NOTES AND UNDER THE  SUBSCRIPTION  AGREEMENT ON
BEHALF OF THE HOLDERS OF NOTES.

                                 HYBRIDON, INC.


                       Class G Warrant for the Purchase of

                                 Notes due 2002


No. G-1                                                $387,100 principal amount
                                                               of Notes due 2002


                  FOR VALUE  RECEIVED,  HYBRIDON,  INC., a Delaware  corporation
(the "Company"), hereby certifies that Pillar Investments Ltd. or its registered
assigns (the "Holder") is entitled to purchase from the Company,  subject to the
provisions of this Warrant (the "Warrant"), at any time on or after December 13,
1999 (the "Initial Exercise Date"),  and prior to 5:00 P.M., New York City time,
on November  30,  2006 (the  "Termination  Date"),  three  hundred  eighty-seven
thousand  one  hundred  dollars  ($387,100)  principal  amount of Notes due 2002
("Notes") of the Company, at an exercise price of one hundred ten percent (110%)
of such Notes' principal amount, for an aggregate exercise price of four hundred
twenty-five  thousand  eight  hundred  ten  dollars  ($425,810)  (the  aggregate
purchase price payable for the Warrant Notes hereunder is hereinafter  sometimes
referred to as the "Aggregate Exercise Price").  The Notes deliverable upon such
exercise  are  hereinafter  sometimes  referred to as the  "Warrant  Notes." The
exercise  price per dollar  principal  amount of Notes (i.e.  one dollar and ten
cents ($1.10)) is hereinafter  sometimes referred to as the "Per Dollar Exercise
Price."


                                       24
<PAGE>

                  1.       Exercise of Warrant.

                  (a) This Warrant may be exercised in whole or in part,  at any
time by its Holder  commencing  on the  Initial  Exercise  Date and prior to the
Termination  Date by presentation  and surrender of this Warrant,  together with
the duly executed  subscription  form attached at the end hereof, at the address
set forth in Subsection  8(a) hereof,  together  with  payment,  by certified or
official bank check or wire transfer payable to the order of the Company, of the
Aggregate Exercise Price or the proportionate part thereof if exercised in part.

                  (b) If this  Warrant is  exercised  in part only,  the Company
shall, upon presentation of this Warrant upon such exercise, execute and deliver
(along with the  certificate  for the  Warrant  Notes  purchased)  a new Warrant
evidencing  the  rights of the  Holder  hereof to  purchase  the  balance of the
Warrant Notes purchasable hereunder upon the same terms and conditions as herein
set forth.  Upon proper  exercise of this Warrant,  the Company  promptly  shall
deliver the  Warrant  Notes to the Holder duly  legended  as  authorized  by the
subscription form.

                  (c) The  execution of this Warrant shall also  constitute  the
Holder's  agreement to be bound by the terms of a  Subscription  Agreement and a
Subordination  and Intercreditor  Agreement,  copies of which are available from
the Company.

                  2.  Reservation of Warrant Shares;  Fully Paid Shares;  Taxes.
The Company hereby  represents that it has, and until expiration of this Warrant
agrees that it shall,  reserve for  issuance or delivery  upon  exercise of this
Warrant, such number of Notes and such number of shares of Common Stock as shall
be required  for  issuance  and/or  delivery  upon  exercise of this Warrant and
conversion of the Notes  issuable upon exercise  hereof in full, and agrees that
all Warrant Notes and shares of Common Stock so issued and/or  delivered will be
validly  issued,  fully paid and  non-assessable,  and further agrees to pay all
taxes and charges that may be imposed upon such issuance and/or delivery.

                  3.       [Reserved.]

                  4.  Limited  Transferability.  This  Warrant  may not be sold,
transferred,  assigned or  hypothecated  by the Holder except in compliance with
the provisions of the Act and the applicable  state  securities "blue sky" laws,
and is so  transferable  only upon the books of the Company which it shall cause
to be maintained for such purpose.  The Company may treat the registered  Holder
of this  Warrant as he or it appears on the  Company's  books at any time as the
Holder for all purposes. The Company shall permit any Holder of a Warrant or his
duly authorized  attorney,  upon written request during ordinary business hours,
to inspect  and copy or make  extracts  from its books  showing  the  registered
holders of Warrants. All Warrants issued upon the transfer or assignment of this
Warrant  will be dated  the same  date as this  Warrant,  and all  rights of the
holder thereof shall be identical to those of the Holder.

                  5.  Loss,   etc.,   of  Warrant.   Upon  receipt  of  evidence
satisfactory  to the Company of the loss,  theft,  destruction  or mutilation of
this Warrant, and of indemnity reasonably  satisfactory to the Company, if lost,
stolen or destroyed,  and upon surrender and

                                        2
<PAGE>

cancellation  of this  Warrant,  if  mutilated,  the Company  shall  execute and
deliver to the Holder a new Warrant of like date, tenor and denomination.

                  6.       Investment Intent.

                  (a) The Holder represents,  by accepting this Warrant, that it
understands  that this Warrant and any  securities  obtainable  upon exercise of
this Warrant have not been registered for sale under Federal or state securities
laws and are  being  offered  and  sold to the  Holder  pursuant  to one or more
exemptions  from the  registration  requirements  of such  securities  laws. The
Holder is an "accredited  investor" within the meaning of Regulation D under the
Securities  Act of 1933, as amended (the "Act").  In the absence of an effective
registration of such securities or an exemption therefrom,  any certificates for
such securities shall bear the legend set forth on the subscription form hereof.
The Holder  understands that it must bear the economic risk of its investment in
this Warrant and any securities  obtainable upon exercise of this Warrant for an
indefinite  period of time,  as this Warrant and such  securities  have not been
registered  under Federal or state  securities laws and therefore cannot be sold
unless  subsequently  registered under such laws,  unless as exemption from such
registration is available.

                  (b) The Holder, by his acceptance of this Warrant,  represents
to the Company  that it is  acquiring  this  Warrant and will  acquire any Notes
obtainable  upon  exercise  of this  Warrant  and any  shares  of  Common  Stock
obtainable  upon conversion of such Notes for its own account for investment and
not with a view to, or for sale in connection with, any distribution  thereof in
violation of the Act. The Holder agrees that this Warrant and any such Notes and
Common Stock will not be sold or otherwise transferred unless (i) a registration
statement  with  respect to such  transfer  is  effective  under the Act and any
applicable  state securities laws or (ii) such sale or transfer is made pursuant
to one or more exemptions from the Act.

                  7.  Status of Holder.  This  Warrant  does not confer upon the
Holder any right to vote or to consent to or receive  notice as a stockholder of
the Company, as such, in respect of any matters whatsoever,  or any other rights
or liabilities as a stockholder, prior to the exercise hereof.

                  8.  Notices.  No  notice  or other  communication  under  this
Warrant shall be effective unless, but any notice or other  communication  shall
be  effective  and shall be deemed to have been given if, the same is in writing
and is mailed by first-class mail, postage prepaid, addressed to:

                  (a)  the   Company   at  155   Fortune   Boulevard,   Milford,
         Massachusetts,  01757  Attention:  E. Andrews  Grinstead,  III, or such
         other  address as the Company has  designated in writing to the Holder;
         or

                  (b) the  Holder  at  Pillar  Investments  Ltd.,  28  Avenue de
         Messine,  Paris,  France 75008 or such other  address as the Holder has
         designated in writing to the Company.

                  9.  Headings.  The headings of this Warrant have been inserted
as a matter of convenience and shall not affect the construction hereof.


                                       3
<PAGE>

                  10.  Applicable  Law.  This  Warrant  shall be governed by and
construed  in  accordance  with  the law of the  Commonwealth  of  Massachusetts
without giving effect to principles of conflicts of law thereof.

                                       4

<PAGE>


                  IN WITNESS WHEREOF, E. Andrews Grinstead,  III, acting for and
on behalf of the  Company,  has executed  this Warrant and caused the  Company's
corporate seal to be hereunto affixed and attested by its Secretary or Assistant
Secretary as of December __, 1999.

                                         HYBRIDON, INC.


                                         By:____________________________________
                                            Name:  E. Andrews Grinstead, III
                                            Title: President and Chief Executive
                                                   Officer

ATTEST:


--------------------------------
Secretary or Assistant Secretary

[Corporate Seal]

                                       5

<PAGE>


                                  SUBSCRIPTION

                  The undersigned, ____________________________, pursuant to the
provisions  of the  foregoing  Warrant,  hereby  elects to  exercise  the within
Warrant to the extent of purchasing $_________________ principal amount of Notes
due 2002 thereunder and hereby makes payment of $_______________ by certified or
official bank check in payment of the exercise price  therefor.  The undersigned
further consents to the placement of the following legends on such Notes:

         THE  TERMS OF THIS  NOTE ARE  SUBJECT  TO THE  TERMS OF A  SUBSCRIPTION
         AGREEMENT AND AN INTERCREDITOR AGREEMENT, COPIES OF WHICH ARE AVAILABLE
         FROM HYBRIDON, INC. (THE "COMPANY"). THE SECURITIES REPRESENTED BY THIS
         NOTE HAVE NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES ACT OF
         1933,  AS AMENDED  (THE  "SECURITIES  ACT"),  OR ANY  APPLICABLE  STATE
         SECURITIES  LAWS,  AND MAY NOT BE SOLD,  OFFERED  FOR SALE,  PLEDGED OR
         HYPOTHECATED OR OTHERWISE  TRANSFERRED IN THE ABSENCE OF A REGISTRATION
         STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES UNDER THE SECURITIES
         ACT OR AN EXEMPTION FROM THE SECURITIES ACT. ANY SUCH TRANSFER MAY ALSO
         BE SUBJECT TO COMPLIANCE WITH APPLICABLE  STATE SECURITIES LAWS AND THE
         LAWS OF OTHER APPLICABLE JURISDICTIONS.

         THE SECURED  PARTY (AS DEFINED IN THE  SUBSCRIPTION  AGREEMENT)  IS THE
         EXCLUSIVE  AGENT OF THE  HOLDER OF THIS NOTE WITH  RESPECT  TO  CERTAIN
         ACTIONS  HEREUNDER AND UNDER THE  SUBSCRIPTION  AGREEMENT;  THE SECURED
         PARTY, IN ITS SOLE DISCRETION, MAY TAKE OR FOREBEAR FROM TAKING CERTAIN
         ACTIONS HEREUNDER AND UNDER THE SUBSCRIPTION AGREEMENT ON BEHALF OF THE
         HOLDERS OF NOTES.



Dated:_______________                   Signature:_____________________________


         Address:_______________________________


                                       6


<PAGE>


                                   ASSIGNMENT

                  FOR  VALUE  RECEIVED   _______________________________________
hereby sells,  assigns and transfers unto  _____________________________________
the foregoing  Warrant and all rights  evidenced  thereby,  and does irrevocably
constitute and appoint _____________________________, attorney, to transfer said
Warrant on the books of Hybridon, Inc.

Dated:_______________                   Signature:_____________________________


         Address:______________________________




                               PARTIAL ASSIGNMENT

                  FOR VALUE RECEIVED  __________________________  hereby assigns
and transfers unto  _________________________  the right to purchase $__________
principal  amount of Notes due 2002 of Hybridon,  Inc.  covered by the foregoing
Warrant,  and a  proportionate  part of said  Warrant  and the rights  evidenced
thereby, and does irrevocably constitute and appoint __________________________,
attorney, to transfer that part of said Warrant on the books of Hybridon, Inc.

Dated:_______________                     Signature:___________________________


         Address:_____________________________


                                       7