Document:

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                                                                    EXHIBIT 10.1

                                 HYBRIDON, INC.

                      NON-STATUTORY STOCK OPTION AGREEMENT
                     (FOR 3,150,000 SHARES OF COMMON STOCK)

         This Non-Statutory Stock Option Agreement ("Agreement") between
Hybridon, Inc., a Delaware corporation, and the Executive, Stephen R. Seiler, is
effective as of July 25, 2001 ("Effective Date"). This Agreement evidences the
grant of a nonqualified stock option to the Executive effective as of the
Effective Date, subject to the terms and conditions herein.

     1.   DEFINITIONS. All capitalized terms that are not otherwise defined in
this Agreement shall have the meanings set forth below:

          (a)  BOARD means the Board of Directors of Hybridon, Inc.

          (b)  CAUSE means the Executive's (i) material breach of any material
terms of the Employment Agreement, (ii) plea of guilty or nolo contendre to, or
conviction of, the commission of a felony offense, (iii) repeated unexplained or
unjustified absence, or refusals to carry out the lawful directions of the
Board, or (iv) material breach of a fiduciary duty owed to the Company under the
Employment Agreement, provided that any action or inaction described by (i),
(iii), or (iv), above, shall not be the basis of a termination of the
Executive's employment with the Company for "Cause" unless the Company provided
the Executive with at least twenty days advance written notice specifying in
reasonable detail the conduct in need of being cured and such conduct was not
cured within the notice period.

          (c)  CHANGE OF CONTROL means the occurrence of any of the following
events:

               (i)  a change in ownership or control of the Company effected
through either of the following transactions:

                    (A)  any "person" (as such term is used in Sections 13(d)
and 14(d) of the Exchange Act), other than a current stockholder of the Company
or a trustee or other fiduciary holding securities of the Company under an
employee benefit plan maintained by the Company or any corporation owned,
directly or indirectly, by the Company's stockholders in substantially the same
proportions as their ownership of the Company's stock, becomes the "beneficial
owner" (as defined in Rule 13d-3 under the Exchange Act), directly or
indirectly, of securities of the Company representing 50% or more of the total
combined voting power of the Company's then-outstanding securities pursuant to a
tender or exchange offer made directly to the Company's stockholders and which
the Board does not recommend such stockholders to accept; or

                    (B)  a change in the composition of the Board over a period
of thirty-six consecutive months or less such that a majority of the members of
the Board ceases to be comprised of individuals who are Continuing Members; for
such purpose, a "Continuing Member" means an individual who is a member of the
Board on the date of the Employment Agreement and any successor of a Continuing
Member who is elected to the Board or nominated for election by action of a
majority of Continuing Members then serving on the Board; or

               (ii) either of the following stockholder-approved transactions to
which the Company is a party:

                    (A)  a merger or consolidation of the Company with any other
corporation other than a merger or consolidation that would result in the voting
securities of the Company outstanding immediately prior thereto continuing to
represent (either by remaining outstanding or by being converted into voting
securities of the surviving or acquiring

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entity) at least 60% of the total voting power represented by the voting
securities of the Company or such surviving entity outstanding immediately after
such merger or consolidation; or

                    (B)  the sale, transfer or complete liquidation or
dissolution of the Company of all or substantially all of the Company's assets.

               (iii) an event not otherwise described in subparagraph (i) or
(ii), above, that is a merger or consolidation of the Company with any other
corporation (other than a corporation controlled by, under common control with
or controlling the Company), a sale or licensing by the Company of all or
substantially all of the assets (including patents, patent applications and
know-how) comprising either the Company's antisense technology or its
immuno-modulatory technology, or a material acquisition by the Company, if, in
connection with any of the events described in this subparagraph (iii), the
Executive either (A) ceases to be employed as the Chief Executive Officer of the
Company or the surviving entity by reason of a termination of employment by the
Company or (B) terminates employment for Good Reason, in either case within six
months of such event.

          (d)  CODE means the Internal Revenue Code of 1986, as amended.

          (e)  COMMON STOCK means common stock of the Company, having $0.001 par
value.

          (f)  COMPANY means Hybridon, Inc., a Delaware corporation.

          (g)  DISABILITY means the inability of the Executive to perform all
the material duties of the Executive's position for a continuous period of at
least 90 days due to a permanent physical or mental impairment, as determined
and certified by a physician selected by the Executive and with the concurrence
of a physician selected by the Company, provided that if the physician selected
by the Executive and the physician selected by the Company do not agree
regarding the determination and certification, a determination and certification
rendered by an independent physician mutually agreed upon by the Executive and
the Company shall be final and binding on the parties with respect to this
Agreement.

          (h)  EMPLOYMENT AGREEMENT means the employment agreement by and
between Stephen R. Seiler and Hybridon, Inc., effective as of July 25, 2001,
including any subsequent amendments.

          (i)  EMPLOYMENT PERIOD means the period during which the Employment
Agreement is in effect, as determined under Section 3 of the Employment
Agreement.

          (j)  EXCHANGE ACT means the Securities Exchange Act of 1934, as
amended.

          (k)  EXECUTIVE, solely for purposes of this Agreement, includes a
Permitted Transferee.

          (l)  FAIR MARKET VALUE means, with respect to any property (including,
without limitation, any shares of Common Stock or other securities of the
Company), the fair market value of such property determined in good faith by
such methods or procedures as shall be established from time to time by the
Board. Notwithstanding the preceding sentence, where there exists a public
market for the Common Stock, the Fair Market Value of a share of Common Stock
shall be the closing price for a share of Common Stock for the last market
trading date prior to the time of the determination (or, if no closing price was
reported on that date, on the last trading date on which a closing price was
reported) on the stock exchange determined by the Board to be the primary market
for the Common Stock, as reported in The Wall Street Journal or such other
source as the Board deems reliable.

                                      -2-

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          (m)  GOOD REASON means the occurrence of one or more of the following:

               (i)  any action by the Company which results in a material
diminution of Executive's position, title, annual base salary, authority, duties
or responsibilities or reporting structure; (ii) any material breach of the
Employment Agreement by the Company which is not remedied by the Company within
30 days after receipt by the Company of notice thereof given by the Executive
specifying in reasonable detail the alleged breach;

               (iii) failure to elect the Executive to serve on the Board during
the Employment Period; or

               (iv) relocation of the Company's headquarters outside Cambridge,
Massachusetts (or within 30 miles therefrom) or 10 miles east of the Worcester
area, except in the event of a change in the location of the headquarters of the
Company to a site within the continental United States following a Change of
Control.

          (n)  OPTION PRICE means the purchase price paid by the Executive for
each share of Common Stock purchased under this Agreement.

          (o)  PARENT means a parent corporation, as such term is defined under
Section 424(e) and (g) of the Code, with respect to the Company.

          (p)  PERMITTED TRANSFEREE means the spouse, mother, father, sister,
brother, or lineal descendant(s) of the Executive named in this Agreement or a
trust established exclusively for the benefit of one or more such individuals.

          (q)  SUBSIDIARY means a subsidiary corporation, as such term is
defined under Section 424(f) and (g) of the Code, with respect to the Company.

     2.   GRANT. The Company hereby grants to the Executive the right (the
"Option") to purchase all or any part of an aggregate of 3,150,000 shares of
Common Stock, subject to adjustment pursuant to Section 9, below. The Option is
in all respects limited and conditioned as provided in this Agreement. This
Option shall be a nonqualified stock option and is not intended to satisfy the
requirements of Section 422 of the Code.

     3.   VESTING. The Executive may exercise the Option in accordance with the
terms of this Agreement, in whole or in part, to the extent that the Executive's
rights under the Option have vested.

          (a)  The Option shall vest as follows, subject to earlier vesting as
described in paragraph (b), below.

         NUMBER OF ADDITIONAL SHARES OF
         COMMON STOCK THAT VEST ON THIS DATE                DATE
         -----------------------------------                ----
                  157,500                                   December 1, 2001
                  157,500                                   March 1, 2002
                  157,500                                   June 1, 2002
                  157,500                                   September 1, 2002
                  157,500                                   December 1, 2002
                  157,500                                   March 1, 2003
                  157,500                                   June 1, 2003
                  157,500                                   September 1, 2003

                                      -3-

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                  157,500                                   December 1, 2003
                  157,500                                   March 1, 2004
                  157,500                                   June 1, 2004
                  157,500                                   September 1, 2004
                  157,500                                   December 1, 2004
                  157,500                                   March 1, 2005
                  157,500                                   June 1, 2005
                  157,500                                   September 1, 2005
                  157,500                                   December 1, 2005
                  157,500                                   March 1, 2006
                  157,500                                   June 1, 2006
                  157,500                                   September 1, 2006

          (b)  Notwithstanding the vesting schedule in paragraph (a), above,
vesting of the Option shall be accelerated as described in this paragraph (b)
upon the occurrence of the following events:

               (i)  CHANGE OF CONTROL. In the event of a Change of Control, the
unvested portion of the Option shall become fully vested and nonforfeitable as
of the date that is ten business days before the effective date of a Change of
Control.

               (ii) TERMINATION OF EMPLOYMENT.

                    (A)  OTHER THAN FOR DEATH, DISABILITY, OR CAUSE. If the
Executive's employment with the Company is terminated by the Company other than
on account of the Executive's death, Disability, or for Cause, the Option shall
vest as of the date of such termination of employment to the extent the Option
would have vested during the following thirty-six months (or portion thereof)
remaining in the Employment Period had the Executive's employment not been
terminated.

                    (B)  DEATH. If the Executive's employment with the Company
is terminated by reason of the Executive's death, the Option shall vest as of
the date of such termination of employment to the extent the Option would have
vested during the following twelve months (or portion thereof) remaining in the
Employment Period had the Executive's employment not been terminated.

                    (C)  DISABILITY. If the Executive's employment with the
Company is terminated by the Company for Disability pursuant to Section 7(a)(ii)
of the Employment Agreement, the Option shall vest as of the date of such
termination of employment to the extent the Option would have vested during the
following twelve months (or portion thereof) remaining in the Employment Period
had the Executive's employment not been terminated.

                    (D)  TERMINATION BY THE EXECUTIVE FOR GOOD REASON. If the
Executive terminates his employment with the Company for Good Reason, the Option
shall vest as of the date of such termination of employment to the extent the
Option would have vested during the following thirty-six months (or portion
thereof) remaining in the Employment Period had the Executive's employment not
been terminated.

                    (E)  TERMINATION FOR CAUSE OR VOLUNTARY RESIGNATION (OTHER
THAN FOR GOOD REASON). If the Executive's employment with the Company is
terminated by the Company for Cause or by the Executive through his voluntary
resignation (other than for Good Reason), the portion of the Option that has not
vested shall terminate as of such termination of employment.

                                      -4-
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                         (iii) BOARD'S DISCRETION. Except as prescribed in
subparagraphs (i) and (ii) above, the Board may, at any time, provide that the
Option shall become immediately vested in full or in part.

     4.   OPTION PRICE. The Option Price of each share of Common Stock covered
by the Option shall be $ 0.84, subject to adjustment pursuant to Section 9,
below.

     5.   TERM. The Option shall expire on July 25, 2011 ("Expiration Date"), to
the extent the Executive has not exercised the Option in full before the
Expiration Date.

     6.   EXERCISE.

          (a)  The Executive may exercise the vested portion of this Option, in
full or in part, before the Expiration Date, provided that if the Executive's
employment or service with the Company or a Parent or Subsidiary is terminated:

               (i)  by the Company, a Parent or a Subsidiary for any reason
other than death, Disability, or for Cause or by the Executive for Good Reason,
the Option shall be exercisable for a period beginning on the termination date
and ending on the earlier to occur of (A) twenty-four months after the effective
date of a termination of Executive's employment or service with the Company or a
Parent or a Subsidiary or (B) the Expiration Date;

               (ii) as a result of the Executive's death or Disability, the
Option shall be exercisable, by the Executive or the person or persons to whom
the Executive's rights under the Option pass by will or applicable law, or if no
such person has such right, the Executive's executors or administrators, for a
period beginning on the termination date and ending on the earlier to occur of
(A) twenty-four months after the effective date of his termination of employment
or service with the Company or a Parent or Subsidiary or (B) the Expiration
Date; or

               (iii) as a result of Executive's voluntary resignation (other
than for Good Reason) or as a result of termination by the Company for Cause,
the Option shall be exercisable for a period beginning on the termination date
and ending on the earlier to occur of (A) twelve months after the effective date
of a termination of Executive's employment or service with the Company or a
Parent or Subsidiary or (B) the Expiration Date.

          (b)  If the Executive wants to exercise the Option, the Executive
shall give written notice, in such form as the Company may from time to time
require, to the Company at its principal office by personal delivery, by
registered or certified mail, or by such other method as the Company may permit.
At minimum, the written notice shall identify the Option being exercised, shall
state the number of shares of Common Stock with respect to which the Option is
being exercised, and shall include payment for the shares of Common Stock with
respect to which the Option is being exercised. The payment for shares of Common
Stock acquired pursuant to the exercise of the Option shall be made at the
principal office of the Company, as described in Section 7, below.

          (c)  Upon the exercise of the Option and upon the receipt by the
Company of the payment for the shares of Common Stock pursuant to the exercise
of the Option, the Company shall deliver or cause to be delivered, within a
reasonable time, to the Executive exercising the Option a certificate or
certificates for the number of shares of Common Stock with respect to which the
Option is exercised. The shares of Common Stock shall be registered in the name
of the exercising Executive or in such name jointly with the Executive as the
Executive may direct in the written notice of exercise.

                                      -5-
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     7.   PAYMENT.

          (a)  The Option Price of shares of Common Stock subject to the Option
and any tax withholding obligations arising as a result of the exercise of any
portion of the Option may be paid in any combination of the following permitted
forms of payment.

               (i)  in United States dollars in cash or by check made payable to
the Company;

               (ii) delivery of an irrevocable and unconditional undertaking by
a creditworthy broker to deliver promptly to the Company sufficient funds to pay
the Option Price or the amount of any applicable withholding taxes, or delivery
by the Executive to the Company of a copy of irrevocable and unconditional
instructions to a creditworthy broker to delivery promptly to the Company cash
or a check sufficient to pay the Option Price or the amount of any applicable
withholding taxes;

               (iii) by surrender of shares of Common Stock having an aggregate
Fair Market Value, as of the date of payment, equal to all or a portion of the
Option Price or the amount of any applicable withholding taxes;

               (iv) by delivery of a promissory note of the Executive to the
Company on terms determined by the Board; or

               (v)  by payment of such other lawful consideration as the Board
may determine.

          (b)  Shares of Common Stock which may be surrendered in satisfaction
of all or any portion of the Option Price or any tax withholding obligation that
results from the exercise of any portion of this Option include shares of Common
Stock covered by the portion of the Option that is being exercised and other
shares of Common Stock held by the Executive; provided that shares of Common
Stock surrendered to pay the Option Price shall be held by the Executive for at
least six months as of the date of payment.

     8.   NONTRANSFERABILITY. The Option shall not be assignable or transferable
by the Executive except by will or by the laws of descent and distribution and
during the lifetime of the Executive shall be exercisable only by the Executive,
except as provided in this Section 8. The Executive may, during his lifetime,
transfer the Option, in whole or in part, to a Permitted Transferee. The
transferred portion of the Option may be exercised only by the person or persons
who acquire a proprietary interest in the Option pursuant to the transfer. The
terms applicable to the transferred portion of the Option shall be the same as
those in effect for the Option under this Agreement immediately prior to the
transfer.

     9.   CAPITAL ADJUSTMENTS.

          (a)  ADJUSTMENTS TO COMMON STOCK. In connection with the occurrence of
any stock split, stock dividend, recapitalization, reorganization, merger
consolidation, combination, exchange of shares, liquidation, spin-off or other
similar change in capitalization or event of the Company, or any distribution to
holders of shares of Common Stock other than a normal cash dividend, the number
and kind of shares of Common Stock issuable under this Option and the Option
Price of the portion of the Option outstanding as of such event shall be
adjusted (or substituted stock options may be made), to the extent the Board
shall determine, in good faith, that such adjustment (or substitution) is
necessary and appropriate, to reflect such event. On the occurrence of a Change
of Control described in Section 1(c)(ii)(A) hereof (and limited to such event),
the Board may provide for the following: (i) that the unexercised portion of the
Option outstanding on the occurrence of a Change of Control described in

                                      -6-
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Section 1(c)(ii)(A) hereof shall be assumed or an equivalent Option be
substituted by the acquiring or succeeding corporation (or an affiliate
thereof), or (ii) that, upon written notice delivered to the Executive, the
unexercised portion of the Option outstanding on the occurrence of a Change of
Control described in Section 1(c)(ii)(A) shall terminate effective as of such
date or as of such earlier date as may be specified by the Board in a written
notice delivered to the Executive, provided that if the Board issues a notice
regarding the termination of the unexercised portion of the Option pursuant to
this clause (ii), the effective date of such termination shall not precede any
vesting acceleration date described in Section 3(b)(i) hereof.

          (b)  BOARD DETERMINATIONS. To the extent that the foregoing
adjustments relate to shares of Common Stock or other securities, such
adjustments shall be made by the Board, whose determination in that respect
shall be final, binding and conclusive; provided that if stock options granted
under the Hybridon, Inc. Amended and Restated 1997 Stock Option Plan ("Plan")
are adjusted in connection with one or more of the events described in this
Section 9, the Option shall be adjusted in a manner that is not less favorable
than adjustments to stock options granted under the Plan.

          10.  AMENDMENT. The Board may amend this Agreement, provided that no
amendment to this Agreement shall become effective before the Board obtains the
Executive's consent to such amendment. In order to fully protect the interests
of the Executive, the Board may correct any defect, supply any omission or
reconcile any inconsistency between the terms of this Agreement and the terms of
the Employment Agreement.

          11.  RIGHTS AS A SHAREHOLDER. Except as otherwise provided by the
Board, the Executive shall have no rights as a shareholder with respect to any
shares of Common Stock covered by this Agreement until becoming the record
holder of such shares.

          12.  NO FRACTIONAL SHARES. No fractional shares of Common Stock shall
be issued or delivered under this Agreement. Any fractional shares shall be
settled in cash, property, or other securities, as determined by the Board.

          13.  REGISTRATION OF SHARES. The Company shall take all such actions
as are necessary to ensure the unrestricted transferability of the shares of
Common Stock issuable upon the exercise, in whole or in part, of the Option,
including as may be required (i) the registration or qualification of the shares
for sale under the federal securities laws and applicable state securities laws,
(ii) listing of the shares on any stock exchange on which the Common Stock is
listed and (iii) securing any other necessary governmental approvals.

          14.  WITHHOLDING. The Executive shall pay to the Company, or make
provision satisfactory to the Board for payment of, any taxes required by law to
be withheld in connection with the exercise of the Option not later than the
date of the event creating the tax liability. The Company may, to the extent
permitted by law, deduct any tax obligations not provided for in the preceding
sentence, from any payment of any kind otherwise due to the Executive.

          15.  NO RIGHT TO CONTINUED EMPLOYMENT OR SERVICE. Nothing in this
Agreement shall be deemed to give the Executive any right to be retained in
employment by, or to continue to provide service to, the Company for any period
of time, and no provision of this Agreement shall be deemed to interfere with
the right of the Company to terminate the employment or service of the Executive
pursuant to the terms of the Employment Agreement or any subsequent agreement
between the Executive and the Company.

          16.  SEVERABILITY. If any provision of this Agreement is, becomes, or
is deemed to be invalid, illegal, or unenforceable in any jurisdiction or as to
the Executive, such provision shall be construed or deemed amended to conform
with applicable laws, or if the provision cannot be so construed or deemed
amended without, in the discretion of the Board, materially altering

                                      -7-
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the intent of the Agreement, such provision shall be severed as to the
jurisdiction or the Executive and the remainder of this Agreement shall remain
in full force and effect.

          17.  NOTICES AND PAYMENTS. Any notice required or permitted to be
given to the Executive under this Agreement shall be in writing and shall be
deemed effective upon personal delivery or upon deposit in the United States
mail with postage and fees prepaid. Any notice or communication required or
permitted to be given to the Company under this Agreement shall be in writing,
addressed to the Secretary of the Company at the Company's principal office and
shall be deemed effective upon personal delivery or upon deposit in the United
States mail with postage and fees prepaid.

          18.  HEADINGS. The headings in this Agreement are for convenience of
reference only and shall not be deemed a part of this Agreement for purposes of
the interpretation or construction of this Agreement.

          19.  GOVERNING LAW. The validity and construction of this Agreement
shall be governed by the laws of the State of Delaware without giving effect to
any conflict of law rules that would require the application of the laws of any
jurisdiction other than the internal laws of the State of Delaware to the rights
and duties of the parties, except to the extent the laws of the State of
Delaware are preempted by federal law.

         IN WITNESS WHEREOF, the Company has caused this Agreement to be duly
executed by an officer of the Company, and the Executive has accepted and signed
this Agreement.

                                                   HYBRIDON, INC.

                                           BY:    /s/ YOUSSEF EL ZEIN
                                                  ----------------------------

                                           TITLE:   VICE CHAIRMAN
                                                  ----------------------------

                                           DATE:    6/7/02
                                                  ----------------------------

ACCEPTED:

/s/ STEPHEN R. SEILER
------------------------------
STEPHEN R. SEILER

DATE:      6/7/02
      -------------------------

                                      -8-<PAGE>
                                                                    EXHIBIT 10.2

                                 HYBRIDON, INC.

                      NON-STATUTORY STOCK OPTION AGREEMENT
                      (FOR 490,000 SHARES OF COMMON STOCK)

         This Non-Statutory Stock Option Agreement ("Agreement") between
Hybridon, Inc., a Delaware corporation, and the Executive, Stephen R. Seiler, is
effective as of July 25, 2001 ("Effective Date"). This Agreement evidences the
grant of a nonqualified stock option to the Executive effective as of the
Effective Date, subject to the terms and conditions herein.

          1.   DEFINITIONS. All capitalized terms that are not otherwise defined
in this Agreement shall have the meanings set forth below:

               (a)  BOARD means the Board of Directors of Hybridon, Inc.

               (b)  CAUSE means the Executive's (i) material breach of any
material terms of the Employment Agreement, (ii) plea of guilty or nolo
contendre to, or conviction of, the commission of a felony offense, (iii)
repeated unexplained or unjustified absence, or refusals to carry out the lawful
directions of the Board, or (iv) material breach of a fiduciary duty owed to the
Company under the Employment Agreement, provided that any action or inaction
described by (i), (iii), or (iv), above, shall not be the basis of a termination
of the Executive's employment with the Company for "Cause" unless the Company
provided the Executive with at least twenty days advance written notice
specifying in reasonable detail the conduct in need of being cured and such
conduct was not cured within the notice period.

               (c)  CHANGE OF CONTROL means the occurrence of any of the
following events:

                    (i)  a change in ownership or control of the Company
effected through either of the following transactions:

                         (A)  any "person" (as such term is used in Sections
13(d) and 14(d) of the Exchange Act), other than a current stockholder of the
Company or a trustee or other fiduciary holding securities of the Company under
an employee benefit plan maintained by the Company or any corporation owned,
directly or indirectly, by the Company's stockholders in substantially the same
proportions as their ownership of the Company's stock, becomes the "beneficial
owner" (as defined in Rule 13d-3 under the Exchange Act), directly or
indirectly, of securities of the Company representing 50% or more of the total
combined voting power of the Company's then-outstanding securities pursuant to a
tender or exchange offer made directly to the Company's stockholders and which
the Board does not recommend such stockholders to accept; or

                         (B)  a change in the  composition  of the Board over a
period of thirty-six consecutive months or less such that a majority of the
members of the Board ceases to be comprised of individuals who are Continuing
Members; for such purpose, a "Continuing Member" means an individual who is a
member of the Board on the date of the Employment Agreement and any successor of
a Continuing Member who is elected to the Board or nominated for election by
action of a majority of Continuing Members then serving on the Board; or

                    (ii) either of the following stockholder-approved
transactions to which the Company is a party:

                         (A)  a merger or  consolidation of the Company  with
any other corporation other than a merger or consolidation that would result in
the voting securities of the Company outstanding immediately prior thereto
continuing to represent (either by remaining outstanding or by being converted
into voting securities of the surviving or acquiring

<PAGE>
entity) at least 60% of the total voting power represented by the voting
securities of the Company or such surviving entity outstanding immediately after
such merger or consolidation; or

                         (B)  the sale, transfer or complete liquidation or
dissolution of the Company of all or substantially all of the Company's assets.

                    (iii) an event not otherwise described in subparagraph (i)
or (ii), above, that is a merger or consolidation of the Company with any other
corporation (other than a corporation controlled by, under common control with
or controlling the Company), a sale or licensing by the Company of all or
substantially all of the assets (including patents, patent applications and
know-how) comprising either the Company's antisense technology or its
immuno-modulatory technology, or a material acquisition by the Company, if, in
connection with any of the events described in this subparagraph (iii), the
Executive either (A) ceases to be employed as the Chief Executive Officer of the
Company or the surviving entity by reason of a termination of employment by the
Company or (B) terminates employment for Good Reason, in either case within six
months of such event.

               (d)  CODE means the Internal Revenue Code of 1986, as amended.

               (e)  COMMON STOCK means common stock of the Company, having
$0.001 par value.

               (f)  COMPANY means Hybridon, Inc., a Delaware corporation.

               (g)  DISABILITY means the inability of the Executive to perform
all the material duties of the Executive's position for a continuous period of
at least 90 days due to a permanent physical or mental impairment, as determined
and certified by a physician selected by the Executive and with the concurrence
of a physician selected by the Company, provided that if the physician selected
by the Executive and the physician selected by the Company do not agree
regarding the determination and certification, a determination and certification
rendered by an independent physician mutually agreed upon by the Executive and
the Company shall be final and binding on the parties with respect to this
Agreement.

               (h)  EMPLOYMENT AGREEMENT means the employment agreement by and
between Stephen R. Seiler and Hybridon, Inc., effective as of July 25, 2001,
including any subsequent amendments.

               (i)  EMPLOYMENT PERIOD means the period during which the
Employment Agreement is in effect, as determined under Section 3 of the
Employment Agreement.

               (j)  EXCHANGE ACT means the Securities Exchange Act of 1934, as
amended.

               (k)  EXECUTIVE, solely for purposes of this Agreement, includes a

Permitted Transferee.

               (l)  FAIR MARKET VALUE means, with respect to any property
(including, without limitation, any shares of Common Stock or other securities
of the Company), the fair market value of such property determined in good faith
by such methods or procedures as shall be established from time to time by the
Board. Notwithstanding the preceding sentence, where there exists a public
market for the Common Stock, the Fair Market Value of a share of Common Stock
shall be the closing price for a share of Common Stock for the last market
trading date prior to the time of the determination (or, if no closing price was
reported on that date, on the last trading date on which a closing price was
reported) on the stock exchange determined by the Board to be the primary market
for the Common Stock, as reported in The Wall Street Journal or such other
source as the Board deems reliable.

                                      -2-
<PAGE>
               (m)  GOOD REASON means the occurrence of one or more of the
following:

                    (i)  any action by the Company which results in a material
diminution of Executive's position, title, annual base salary, authority, duties
or responsibilities or reporting structure; (ii) any material breach of the
Employment Agreement by the Company which is not remedied by the Company within
30 days after receipt by the Company of notice thereof given by the Executive
specifying in reasonable detail the alleged breach;

                    (iii) failure to elect the Executive to serve on the Board
during the Employment Period; or

                    (iv) relocation of the Company's headquarters outside
Cambridge, Massachusetts (or within 30 miles therefrom) or 10 miles east of the
Worcester area, except in the event of a change in the location of the
headquarters of the Company to a site within the continental United States
following a Change of Control.

               (n)  OPTION PRICE means the purchase price paid by the Executive
for each share of Common Stock purchased under this Agreement.

               (o)  PARENT means a parent corporation, as such term is defined
under Section 424(e) and (g) of the Code, with respect to the Company.

               (p)  PERMITTED TRANSFEREE means the spouse, mother, father,
sister, brother, or lineal descendant(s) of the Executive named in this
Agreement or a trust established exclusively for the benefit of one or more such
individuals.

               (q)  SUBSIDIARY means a subsidiary corporation, as such term is
defined under Section 424(f) and (g) of the Code, with respect to the Company.

     2.   GRANT. The Company hereby grants to the Executive the right (the
"Option") to purchase all or any part of an aggregate of 490,000 shares of
Common Stock, subject to adjustment pursuant to Section 9, below. The Option is
in all respects limited and conditioned as provided in this Agreement. This
Option shall be a nonqualified stock option and is not intended to satisfy the
requirements of Section 422 of the Code.

     3.   VESTING. The Executive may exercise the Option in accordance with the
terms of this Agreement, in whole or in part, to the extent that the Executive's
rights under the Option have vested.

          (a)  The Option shall vest as follows, subject to earlier vesting as
described in paragraph (b), below.

        NUMBER OF ADDITIONAL SHARES OF
        COMMON STOCK THAT VEST ON THIS DATE                  DATE
        -----------------------------------                  ----

                  122,500                               December 1, 2001
                  122,500                               March 1, 2002
                  122,500                               June 1, 2002
                  122,500                               September 1, 2002

          (b)  Notwithstanding the vesting schedule in paragraph (a), above,
vesting of the Option shall be accelerated as described in this paragraph (b)
upon the occurrence of the following events:

                                      -3-
<PAGE>
               (i)  CHANGE OF CONTROL. In the event of a Change of Control, the
unvested portion of the Option shall become fully vested and nonforfeitable as
of the date that is ten business days before the effective date of a Change of
Control.

               (ii) TERMINATION OF EMPLOYMENT.

                    (A)  OTHER THAN FOR DEATH, DISABILITY, OR CAUSE. If the
Executive's employment with the Company is terminated by the Company other than
on account of the Executive's death, Disability, or for Cause, the Option shall
vest as of the date of such termination of employment to the extent the Option
would have vested during the following thirty-six months (or portion thereof)
remaining in the Employment Period had the Executive's employment not been
terminated.

                    (B)  DEATH. If the Executive's employment with the Company
is terminated by reason of the Executive's death, the Option shall vest as of
the date of such termination of employment to the extent the Option would have
vested during the following twelve months (or portion thereof) remaining in the
Employment Period had the Executive's employment not been terminated.

                    (C)  DISABILITY. If the Executive's employment with the
Company is terminated by the Company for Disability pursuant to Section 7(a)(ii)
of the Employment Agreement, the Option shall vest as of the date of such
termination of employment to the extent the Option would have vested during the
following twelve months (or portion thereof) remaining in the Employment Period
had the Executive's employment not been terminated.

                    (D)  TERMINATION BY THE EXECUTIVE FOR GOOD REASON. If the
Executive terminates his employment with the Company for Good Reason, the Option
shall vest as of the date of such termination of employment to the extent the
Option would have vested during the following thirty-six months (or portion
thereof) remaining in the Employment Period had the Executive's employment not
been terminated.

                    (E)  TERMINATION FOR CAUSE OR VOLUNTARY RESIGNATION (OTHER
THAN FOR GOOD REASON). If the Executive's employment with the Company is
terminated by the Company for Cause or by the Executive through his voluntary
resignation (other than for Good Reason), the portion of the Option that has not
vested shall terminate as of such termination of employment.

               (iii) BOARD'S DISCRETION. Except as prescribed in subparagraphs
(i) and (ii) above, the Board may, at any time, provide that the Option shall
become immediately vested in full or in part.

     4.   OPTION PRICE. The Option Price of each share of Common Stock covered
by the Option shall be $ 0.71, subject to adjustment pursuant to Section 9,
below.

     5.   TERM. The Option shall expire on July 25, 2011 ("Expiration Date"), to
the extent the Executive has not exercised the Option in full before the
Expiration Date.

     6.   EXERCISE.

          (a)  The Executive may exercise the vested portion of this Option, in
full or in part, before the Expiration Date, provided that if the Executive's
employment or service with the Company or a Parent or Subsidiary is terminated:

                                      -4-
<PAGE>
               (i)  by the Company, a Parent or a Subsidiary for any reason
other than death, Disability, or for Cause or by the Executive for Good Reason,
the Option shall be exercisable for a period beginning on the termination date
and ending on the earlier to occur of (A) twenty-four months after the effective
date of a termination of Executive's employment or service with the Company or a
Parent or a Subsidiary or (B) the Expiration Date;

               (ii) as a result of the Executive's death or Disability, the
Option shall be exercisable, by the Executive or the person or persons to whom
the Executive's rights under the Option pass by will or applicable law, or if no
such person has such right, the Executive's executors or administrators, for a
period beginning on the termination date and ending on the earlier to occur of
(A) twenty-four months after the effective date of his termination of employment
or service with the Company or a Parent or Subsidiary or (B) the Expiration
Date; or

               (iii) as a result of Executive's voluntary resignation (other
than for Good Reason) or as a result of termination by the Company for Cause,
the Option shall be exercisable for a period beginning on the termination date
and ending on the earlier to occur of (A) twelve months after the effective date
of a termination of Executive's employment or service with the Company or a
Parent or Subsidiary or (B) the Expiration Date.

          (b)  If the Executive wants to exercise the Option, the Executive
shall give written notice, in such form as the Company may from time to time
require, to the Company at its principal office by personal delivery, by
registered or certified mail, or by such other method as the Company may permit.
At minimum, the written notice shall identify the Option being exercised, shall
state the number of shares of Common Stock with respect to which the Option is
being exercised, and shall include payment for the shares of Common Stock with
respect to which the Option is being exercised. The payment for shares of Common
Stock acquired pursuant to the exercise of the Option shall be made at the
principal office of the Company, as described in Section 7, below.

          (c)  Upon the exercise of the Option and upon the receipt by the
Company of the payment for the shares of Common Stock pursuant to the exercise
of the Option, the Company shall deliver or cause to be delivered, within a
reasonable time, to the Executive exercising the Option a certificate or
certificates for the number of shares of Common Stock with respect to which the
Option is exercised. The shares of Common Stock shall be registered in the name
of the exercising Executive or in such name jointly with the Executive as the
Executive may direct in the written notice of exercise.

     7.   PAYMENT.

          (a)  The Option Price of shares of Common Stock subject to the Option
and any tax withholding obligations arising as a result of the exercise of any
portion of the Option may be paid in any combination of the following permitted
forms of payment.

               (i)  in United States dollars in cash or by check made payable to
the Company;

               (ii) delivery of an irrevocable and unconditional undertaking by
a creditworthy broker to deliver promptly to the Company sufficient funds to pay
the Option Price or the amount of any applicable withholding taxes, or delivery
by the Executive to the Company of a copy of irrevocable and unconditional
instructions to a creditworthy broker to delivery promptly to the Company cash
or a check sufficient to pay the Option Price or the amount of any applicable
withholding taxes;

                                      -5-
<PAGE>

               (iii) by surrender of shares of Common Stock having an aggregate
Fair Market Value, as of the date of payment, equal to all or a portion of the
Option Price or the amount of any applicable withholding taxes;

               (iv) by delivery of a promissory note of the Executive to the
Company on terms determined by the Board; or

               (v)  by payment of such other lawful consideration as the Board
may determine.

          (b)  Shares of Common Stock which may be surrendered in satisfaction
of all or any portion of the Option Price or any tax withholding obligation that
results from the exercise of any portion of this Option include shares of Common
Stock covered by the portion of the Option that is being exercised and other
shares of Common Stock held by the Executive; provided that shares of Common
Stock surrendered to pay the Option Price shall be held by the Executive for at
least six months as of the date of payment.

     8.   NONTRANSFERABILITY. The Option shall not be assignable or transferable
by the Executive except by will or by the laws of descent and distribution and
during the lifetime of the Executive shall be exercisable only by the Executive,
except as provided in this Section 8. The Executive may, during his lifetime,
transfer the Option, in whole or in part, to a Permitted Transferee. The
transferred portion of the Option may be exercised only by the person or persons
who acquire a proprietary interest in the Option pursuant to the transfer. The
terms applicable to the transferred portion of the Option shall be the same as
those in effect for the Option under this Agreement immediately prior to the
transfer.

     9.   CAPITAL ADJUSTMENTS.

          (a)  ADJUSTMENTS TO COMMON STOCK. In connection with the occurrence of
any stock split, stock dividend, recapitalization, reorganization, merger
consolidation, combination, exchange of shares, liquidation, spin-off or other
similar change in capitalization or event of the Company, or any distribution to
holders of shares of Common Stock other than a normal cash dividend, the number
and kind of shares of Common Stock issuable under this Option and the Option
Price of the portion of the Option outstanding as of such event shall be
adjusted (or substituted stock options may be made), to the extent the Board
shall determine, in good faith, that such adjustment (or substitution) is
necessary and appropriate, to reflect such event. On the occurrence of a Change
of Control described in Section 1(c)(ii)(A) hereof (and limited to such event),
the Board may provide for the following: (i) that the unexercised portion of the
Option outstanding on the occurrence of a Change of Control described in Section
1(c)(ii)(A) hereof shall be assumed or an equivalent Option be substituted by
the acquiring or succeeding corporation (or an affiliate thereof), or (ii) that,
upon written notice delivered to the Executive, the unexercised portion of the
Option outstanding on the occurrence of a Change of Control described in Section
1(c)(ii)(A) shall terminate effective as of such date or as of such earlier date
as may be specified by the Board in a written notice delivered to the Executive,
provided that if the Board issues a notice regarding the termination of the
unexercised portion of the Option pursuant to this clause (ii), the effective
date of such termination shall not precede any vesting acceleration date
described in Section 3(b)(i) hereof.

          (b)  BOARD DETERMINATIONS. To the extent that the foregoing
adjustments relate to shares of Common Stock or other securities, such
adjustments shall be made by the Board, whose determination in that respect
shall be final, binding and conclusive; provided that if stock options granted
under the Hybridon, Inc. Amended and Restated 1997 Stock Option Plan ("Plan")
are adjusted in connection with one or more of the events described in this
Section 9, the Option shall be adjusted in a manner that is not less favorable
than adjustments to stock options granted under the Plan.

                                      -6-
<PAGE>
     10.  AMENDMENT. The Board may amend this Agreement, provided that no
amendment to this Agreement shall become effective before the Board obtains the
Executive's consent to such amendment. In order to fully protect the interests
of the Executive, the Board may correct any defect, supply any omission or
reconcile any inconsistency between the terms of this Agreement and the terms of
the Employment Agreement.

     11.  RIGHTS AS A SHAREHOLDER. Except as otherwise provided by the Board,
the Executive shall have no rights as a shareholder with respect to any shares
of Common Stock covered by this Agreement until becoming the record holder of
such shares.

     12.  NO FRACTIONAL SHARES. No fractional shares of Common Stock shall be
issued or delivered under this Agreement. Any fractional shares shall be settled
in cash, property, or other securities, as determined by the Board.

     13.  REGISTRATION OF SHARES. The Company shall take all such actions as are
necessary to ensure the unrestricted transferability of the shares of Common
Stock issuable upon the exercise, in whole or in part, of the Option, including
as may be required (i) the registration or qualification of the shares for sale
under the federal securities laws and applicable state securities laws, (ii)
listing of the shares on any stock exchange on which the Common Stock is listed
and (iii) securing any other necessary governmental approvals.

     14.  WITHHOLDING. The Executive shall pay to the Company, or make provision
satisfactory to the Board for payment of, any taxes required by law to be
withheld in connection with the exercise of the Option not later than the date
of the event creating the tax liability. The Company may, to the extent
permitted by law, deduct any tax obligations not provided for in the preceding
sentence, from any payment of any kind otherwise due to the Executive.

     15.  NO RIGHT TO CONTINUED EMPLOYMENT OR SERVICE. Nothing in this Agreement
shall be deemed to give the Executive any right to be retained in employment by,
or to continue to provide service to, the Company for any period of time, and no
provision of this Agreement shall be deemed to interfere with the right of the
Company to terminate the employment or service of the Executive pursuant to the
terms of the Employment Agreement or any subsequent agreement between the
Executive and the Company.

     16.  SEVERABILITY. If any provision of this Agreement is, becomes, or is
deemed to be invalid, illegal, or unenforceable in any jurisdiction or as to the
Executive, such provision shall be construed or deemed amended to conform with
applicable laws, or if the provision cannot be so construed or deemed amended
without, in the discretion of the Board, materially altering the intent of the
Agreement, such provision shall be severed as to the jurisdiction or the
Executive and the remainder of this Agreement shall remain in full force and
effect.

     17.  NOTICES AND PAYMENTS. Any notice required or permitted to be given to
the Executive under this Agreement shall be in writing and shall be deemed
effective upon personal delivery or upon deposit in the United States mail with
postage and fees prepaid. Any notice or communication required or permitted to
be given to the Company under this Agreement shall be in writing, addressed to
the Secretary of the Company at the Company's principal office and shall be
deemed effective upon personal delivery or upon deposit in the United States
mail with postage and fees prepaid.

     18.  HEADINGS. The headings in this Agreement are for convenience of
reference only and shall not be deemed a part of this Agreement for purposes of
the interpretation or construction of this Agreement.

                                      -7-

<PAGE>
     19.  GOVERNING LAW. The validity and construction of this Agreement shall
be governed by the laws of the State of Delaware without giving effect to any
conflict of law rules that would require the application of the laws of any
jurisdiction other than the internal laws of the State of Delaware to the rights
and duties of the parties, except to the extent the laws of the State of
Delaware are preempted by federal law.

         IN WITNESS WHEREOF, the Company has caused this Agreement to be duly
executed by an officer of the Company, and the Executive has accepted and signed
this Agreement.

                                                HYBRIDON, INC.

                                 BY:  /s/ YOUSSEF EL ZEIN
                                     ---------------------------------------

                              TITLE:       VICE CHAIRMAN
                                     ---------------------------------------

                              DATE:        6/7/02
                                     ---------------------------------------

ACCEPTED:

/s/ STEPHEN R. SEILER
--------------------------------
STEPHEN R. SEILER

DATE:     6/7/02
      --------------------------

                                      -8-

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