Exhibit 10(yy)

                     AMENDMENT NO. 4 TO EMPLOYMENT AGREEMENT

            This AMENDMENT NO. 4 TO EMPLOYMENT AGREEMENT (this "Amendment No.
4"), dated as of October 1, 2002 (the "Effective Date of Amendment No. 4"),
between SIGA Technologies, Inc., a Delaware corporation (the "Corporation"), and
Dr. Dennis E. Hruby ("Hruby"), amends and waives certain provisions of the
Employment Agreement, dated as of January 1, 1998, as amended by the Amendment,
dated as of October 18, 1999, Amendment No. 2, dated as of June 13, 2000, and
Amendment No. 3, dated as of January 31, 2002, between the Corporation and Hruby
(the "Existing Agreement"). Capitalized terms used but not defined herein shall
have the respective meanings assigned to them in the Existing Agreement.

            WHEREAS, under the Existing Agreement, the Initial Term ends on
      December 31, 2002; and

            WHEREAS, the Corporation and Hruby desire to amend the Existing
      Agreement as provided in this Amendment No. 4.

            NOW THEREFORE, in consideration of the premises and for other good
and valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, the undersigned, intending legally to be bound, hereby agree as
follows:

            1. Section 2 of the Existing Agreement (referenced as "Paragraph 1"
in the Amendment No. 2, dated as of June 13, 2000) shall be amended to read in
its entirety as follows:

                  2. Employment for Term. The Corporation hereby employs Hruby
      and Hruby hereby accepts employment with the Corporation for the period
      beginning on the date of this Agreement and ending December 31, 2005 (the
      "Initial Term"), or upon the earlier termination of the Term pursuant to
      Section 7. The foregoing notwithstanding, the Corporation shall have the
      right to terminate Hruby's employment under the Agreement upon 1 year
      written notice and such termination will be treated as Termination with
      Cause pursuant to Section 8 of this Agreement. The termination of Hruby's
      employment under this Agreement shall end the Term but shall not terminate
      Hruby's or the Corporation's other agreements in this Agreement, except as
      otherwise provided herein.

            2. Section 4(a) of the Existing Agreement shall be amended to add
the following sentence at the end thereof:

      From and after the closing date of the Corporation's financing
      contemplated by that certain Private Placement Memorandum, dated July 24,
      2002 relating to the sale by the Corporation of certain units consisting
      of Common Stock and Warrants to purchase Common Stock, the Base Salary
      shall be not less than $210,000 per annum, and the Corporation shall make
      the appropriate adjustments to its payroll.

            3. Subsection 4(d) of the Existing Agreement shall be deleted, be of
no further force and effect, and be replaced by the following:

<PAGE>

            (d) 2002 Stock Option Grant. Hruby shall be granted (the "A4 Option
      Grant") an option to purchase a total of 300,000 shares of Common Stock of
      the Corporation at an exercise price of $2.50 per share, which shall vest
      with respect to 75,000 shares immediately and with respect to an
      additional 75,000 shares on September 1 of each of 2003, 2004 and 2005,
      pursuant to a Stock Option Grant Agreement in substantially the form
      attached hereto as Exhibit A4A. Simultaneously with the A4 Option Grant,
      Hruby shall surrender to the Corporation the Incentive Stock Option Grant
      Agreement, dated as of January 31, 2002, with respect to an option to
      purchase up to 50,000 shares of Common Stock of the Corporation at an
      exercise price of $3.94 per share (the "January Option"); and the
      Corporation shall cancel the January Option.

            4. Section 4 of the Existing Agreement shall be amended to add a
Subsection (e) that reads as follows:

            (e) Other and Additional Compensation. The preceding sections
      establish the minimum compensation during the Term and shall not preclude
      the Board from awarding Hruby a higher salary or any bonuses or stock
      options in the discretion of the Board during the Term at any time,
      provided that, from and after the Effective Date of Amendment No. 4, any
      bonus amount awarded Hruby in the discretion of the Board shall not exceed
      30% of Hruby's annual salary.

            5. Subsection 8(d) of the Existing Agreement shall be amended to
read in its entirety as follows:

            (d) Change of Control Payment. The provision of this Subsection 8(d)
      set forth the terms of an agreement reached between Hruby and the
      Corporation regarding Hruby's rights and obligations upon the occurrence
      of a "Change in Control" (as hereinafter defined) of the Corporation.
      These provisions are intended to assure and encourage in advance Hruby's
      continued attention and dedication to his assigned duties and his
      objectivity during the pendency and after the occurrence of any such
      Change in Control. These provisions shall apply in lieu of, and expressly
      supersede, the provisions of Subsection 8(c) if Kruby's employment is
      terminated or Notice of Termination is given ninety (90) days prior to or
      within twelve (12) months after the occurrence of an event constituting a
      Change in Control.

            (i) Escrow. Within ten (10) days after the occurrence of the first
      event constituting a Change in Control (irrespective of whether Hruby has
      actual knowledge of such event), the Corporation shall place immediately
      negotiable funds in escrow in an amount equal to the lesser of (A) Hruby's
      salary and all other amounts due hereunder for the remainder of the Term,
      plus such additional amount as equals the "Gross Up Payment" (as
      hereinafter defined) thereon (the "Change of Control Amount") and (B) the
      amount of Hruby's annual base salary at such time. Such escrow shall be
      conducted pursuant to a standard escrow agreement among the Corporation,
      Hruby and an independent escrow agent providing for the timely payment to
      Hruby of the amounts hold in such escrow in the event Hruby becomes


                                      -2-
<PAGE>

      entitled thereto under the applicable provisions of this Agreement (the
      "Escrow Arrangement"). The Escrow Arrangement shall be maintained until
      the earlier of (A) twelve months and one day after the occurrence o(pound)
      an event constituting a Change in Control or (B) the payment to Hruby of
      all sums escrowed.

            (ii) Change in Control. If, within 90 days prior to, or within
      eighteen (18) months after the occurrence of an event constituting a
      Change in Control, Hruby's employment is terminated or a Notice of
      Termination is given for any reason other than (A) his death, (B) his
      Disability, or (C) by Hruby, then such termination shall be deemed to be a
      "Termination Due to Change in Control (herein so called), in which event
      the Corporation shall pay Hruby, in a lump sum, on or prior to the fifth
      (5th) day following the date of termination of the Term:

                  (A) an amount equal to the Change of Control Amount (including
                  any Gross Up Payment); and

                  (B) Hruby's accrued and unpaid base salary.

            (iii) Stock Option Floor. Upon the occurrence of the first event
      constituting a Change in Control, all stock options and other stock-based
      grants to Hruby by the Corporation shall, irrespective of any provisions
      of his option agreements, immediately and irrevocably vest and become
      exercisable as of the date of such first event whereupon, at any time
      during the Option Term as defined in the option agreements, Hruby or his
      estate may by five (5) days' advance written notice given to the
      Corporation, and irrespective of whether Hruby is then employed by the
      Corporation or then living, and solely at the election of Hruby or his
      estate, require the Corporation to:

                  (A) within thirty (30) days of a request by Hruby or his
                  estate file and cause to become effective a Form S-8 (or other
                  appropriate form) with the Securities and Exchange Commission
                  ("SEC') registering for resale all shares underlying stock
                  options granted to Hruby and outstanding with all fees and
                  expenses of such filing being paid by the Corporation; or

                  (B) allow Hruby to exercise all or any part of such Stock
                  Options at the option prices therefor specified in the grant
                  of the Stock Options,

            (iv) Gross Up Payment.

                  (A) Excess Parachute Payment. If Hruby incurs the tax (the
                  "Excise Tax") imposed by Section 4999 of the Internal Revenue
                  Code of 1986 (the "Code") on "Excess Parachute Payments"
                  within the meaning of Section 28OG(b)(1) of the


                                      -3-
<PAGE>

                  Code, the Corporation will pay to Hruby an amount (the "Gross
                  Up Payment") such that the net amount retained by Hruby, after
                  deduction of any Excise Tax on both the Excess Parachute
                  Payment and any federal, state and local income tax (together
                  with penalties and interest) as well as the Excise Tax upon
                  the payment provided for by this Subparagraph 8(d)(iv)(A),
                  will be equal to the Change of Control Amount.

                  (B) Applicable Rates. For purposes of determining the amount
                  of the Gross Up Payment, Hruby will be deemed to pay federal
                  income taxes at the highest marginal rate of federal income
                  taxation in the calendar year in which the Gross Up Payment is
                  to be made and state and local income taxes at the highest
                  marginal rates of taxation in the state and locality where
                  taxes thereon are lawfully due, net of the maximum reduction
                  (if any) in federal income taxes that could be obtained from
                  deduction of deductible state and local taxes.

                  (C) Determination of Gross Up Payment Amount. The
                  determination of whether the Excise Tax is payable and the
                  amount thereof will be based upon the opinion of tax counsel
                  selected by Hruby and reasonably approved by the Corporation,
                  which approval will not be unreasonably withheld or delayed.
                  If such opinion is not finally accepted by the Internal
                  Revenue Service (or state and local taxing authorities), then
                  appropriate adjustments to the Excise Tax will be computed and
                  additional Gross Up Payments will be made in the manner
                  provided by this Paragraph 8(d)(iv).

                  (D) Payment. The Corporation will pay the estimated amount of
                  the Gross Up Payment in cash to Hruby at the time specified in
                  this Agreement. Hruby and the Corporation agree to reasonably
                  cooperate in the determination of the actual amount of the
                  Gross Up Payment. Further, Hruby and the Corporation agree to
                  make such adjustments to the estimated amount of the Gross Up
                  Payment as may be necessary to equal the actual amount of the
                  Gross Up Payment, which in the case of the Corporation will
                  refer to refunds of prior overpayments by the Corporation and
                  in the case of Hruby will refer to additional payments to
                  Hruby to make up for prior underpayments.

            (v) Definitions. For purposes of this paragraph 8, the following
      terms shall have the following meanings:

                  (A) "Change in Control" shall mean any of the following:


                                      -4-
<PAGE>

            (1)   the acquisition by any individual, entity, or group (within
                  the meaning of Section 13(d)(3) or 14(d)(2) of the Exchange
                  Act) (the "Acquiring Person"), other than the Corporation, or
                  any of its Subsidiaries or any Excluded Group (as defined
                  herein), of beneficial ownership (within the meaning of Rule
                  l3d-3 promulgated under the Exchange Act) of 35% or more of
                  the combined voting power or economic interests of the then
                  outstanding voting securities of the Corporation entitled to
                  vote generally in the election of directors; provided however,
                  that any transfer from any director or executive officer
                  listed in the Company's Form 10-KSB for the year ended
                  December 31, 2001 under "Security Ownership of Certain
                  Beneficial Owners" (the "Excluded Group") will not result in a
                  Change in Control if such transfer was part of a series of
                  related transactions the effect of which, absent the transfer
                  to such Acquiring Person by the Excluded Group, would not have
                  resulted in the acquisition by such Acquiring Person of 35% or
                  more of the combined voting power or economic interests of the
                  then outstanding voting securities; or

            (2)   during any period of 12 consecutive months after the Effective
                  Date of Amendment No. 4, the individuals who at the beginning
                  of any such 12-month period constituted a majority of the
                  Directors (the "Incumbent Non-Investor Majority") cease for
                  any reason to constitute at least a majority of such
                  Directors; provided that (i) any individual becoming a
                  director whose election, or nomination for election by the
                  Corporation's stockholders, was approved by a vote of the
                  stockholders having the right to designate such director and
                  (ii) any director whose election to the Board or whose
                  nomination for election by the stockholders of the Corporation
                  was approved by the requisite vote of directors entitled to
                  vote on such election or nomination in accordance with the
                  Restated Certificate of Incorporation of the Corporation,
                  shall, in each such case, be considered as though such
                  individual were a member of the Incumbent Non-Investor
                  Majority, but excluding, as a member of the Incumbent
                  Non-Investor Majority, any such individual whose initial
                  assumption of office, is in connection with an actual or
                  threatened election contest relating to the election of the
                  directors of the Corporation (as such terms are used in Rule
                  14a-2 of Regulation 14A promulgated under the Exchange


                                      -5-
<PAGE>

                  Act) and further excluding any person who is an affiliate or
                  associate of an Acquiring Person having acquired within the
                  preceding 12 months, or proposing to acquire, beneficial
                  ownership of 25% or more of the combined voting power of the
                  then outstanding voting securities of the Corporation entitled
                  to vote generally in the election of directors; or

            (3)   the approval by the stockholders of the Corporation of a
                  reorganization, merger or consolidation, in each case, with
                  respect to which all or substantially all of the individuals
                  and entities who were the respective beneficial owners of the
                  voting securities of the Corporation immediately prior to such
                  reorganization, merger, or consolidation do not, following
                  such reorganization, merger, or consolidation, beneficially
                  own, directly or indirectly, more than 50% of the combined
                  voting power of the then outstanding voting securities
                  entitled to vote generally in the election of directors of.
                  the Corporation resulting from such reorganization, merger, or
                  consolidation; or

            (4)   the sale or other disposition of assets representing 50% or
                  more of the assets of the Corporation in one transaction or
                  series of related transactions not initiated or commenced by
                  any person within the Excluded Group; or

            (5)   a "Fundamental Change in Business" as hereinafter defined; or

            (6)   a "Hostile Takeover" as hereinafter defined is declared.

            (B)   "Fundamental Change in Business" shall mean that the
            Corporation, at any time, no longer spends at least fifty percent
            (50%) of its annual budget on activities related to biotechnology or
            pharmaceuticals.

            (C)   "Hostile Takeover" shall mean any Change in Control which at
            any time is declared by at least a majority of the Board, directly
            or indirectly, to be hostile or not in the best interests of the
            Corporation, or in which an attempt is made (irrespective of whether
            successful) to wrest control away from the incumbent management of
            the Corporation and, with respect to which, the Board makes efforts
            to resist.


                                      -6-
<PAGE>

            (vi) Satisfactory Alternative. Notwithstanding anything to the
      contrary herein, Hruby shall have no rights and the Corporation shall have
      no obligation under this Subsection 8(d) with respect to a Termination Due
      to Change in Control if, prior to or simultaneously with such Termination
      Due to Change in Control, Hruby is offered employment within 50 miles of
      Albany Oregon by another business at a level of compensation equal to or
      greater than his compensation hereunder.

            6. The Existing Agreement shall be amended to add an Exhibit A4A
thereto in the form of Exhibit A4A hereto.

            7. Any event occurring prior to the Effective Date of Amendment No.
4 that would otherwise constitute a Change of Control shall not be deemed a
Change of Control for purposes of the Agreement.

            8. Neither the amendments set forth in this Amendment No. 4, nor any
event that took place prior to the Effective Date of Amendment No. 4, shall be
deemed to constitute a breach of the Existing Agreement by the Corporation.

                      [Signature page follows immediately.]


                                      -7-
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have executed this Amendment
No. 4 as of October 1, 2002.

                                        SIGA TECHNOLOGIES, INC.


                                        By: /s/ Thomas N. Konatich
                                            ------------------------------------
                                            Name: Thomas N. Konatich
                                            Title: Acting Chief Executive
                                            Officer, Chief Financial Officer
                                            and Secretary


                                        /s/ Dennis E. Hruby
                                        ----------------------------------------
                                        Dr. Dennis E. Hruby


                                      -8-
<PAGE>

                                                                     EXHIBIT A4A

                             SIGA TECHNOLOGIES, INC.

                        Incentive Stock Option Agreement

                                                 Granting Date: _______ __, ____

To: Dr. Dennis E. Hruby

            We are pleased to notify you that SIGA TECHNOLOGIES, INC., a
Delaware corporation (the "Company") has granted to you (the "Holder") an
incentive stock option (the "Option") under the Company's Amended and Restated
1996 Incentive and Non-Qualified Stock Option Plan (the "Plan") to purchase all
or any part of an aggregate of 300,000 shares of Common Stock of the Company
(the "Optioned Shares"), subject to the terms and conditions of this Agreement.

            1. Vesting, Term and Exercise of Option. Subject to the provisions
of this Agreement, this Option may be exercised for up to the number of vested
Optioned Shares (subject to adjustment as provided in Section 6 hereof) by you
on or prior to the tenth anniversary of the Granting Date ("Last Exercise Date")
at an initial exercise price (the "Exercise Price") of $2.50 per share (subject
to adjustment as provided in Section 6 hereof) and all as subject to Plan and
this Agreement. The Holder may exercise this Option according to the following
vesting schedule: this Option shall be immediately exerciseable with respect to
75,000 Optioned Shares; this Option shall cumulatively vest with respect to
75,000 shares on each of September 1, 2003, September 1, 2004 and September 1,
2005. Any portion of the Option that you do not exercise shall accumulate and
can be exercised by you any time prior to the Last Exercise Date. You may not
exercise your Option to purchase a fractional share or fewer than 100 shares,
and you may only exercise your Option by purchasing shares in increments of 100
shares unless the remaining shares purchasable are less than 100 shares.

            This Option may be exercised by delivering to the Secretary of the
Company (i) a written Notice of Intention to Exercise in the form attached
hereto as Appendix A signed by you and specifying the number of Optioned Shares
you desire to purchase, (ii) payment, in full, of the Exercise Price for all
such Optioned Shares in cash, certified check, surrender of shares of Common
Stock of the Company having a value equal to the exercise price of the Optioned
Shares as to which you are exercising this Option, provided that such
surrendered shares, if previously acquired by exercise of a Company stock
option, have been held by you at least six months prior to their surrender, or
by means of a brokered cashless exercise. As a holder of an option, you shall
have the rights of a shareholder with respect to the Optioned Shares only after
they shall have been issued to you upon the exercise of this Option. Subject to
the terms and provisions of this Agreement and the Plan, the Company shall use
its best efforts to cause the Optioned Shares to be issued as promptly as
practicable after receipt of your Notice of Intention to Exercise.

            2. Non-transferability of Option. This Option shall not be
transferable and may be exercised during your lifetime only by you. Any
purported transfer or assignment of this Option shall be void and of no effect,
and shall give the Company the right to terminate this Option as of the date of
such purported transfer or assignment. No transfer of an Option by will or by
the laws of descent and distribution shall be effective unless the Company shall
have been furnished with

<PAGE>

written notice thereof, and such other evidence as the Company may deem
necessary to establish the validity of the transfer and conditions of the
Option, and to establish compliance with any laws or regulations pertaining
thereto.

            3. Certain Rights and Restrictions With Respect to Common Stock. The
Optioned Shares which you may acquire upon the exercise of this Option will not
be registered under the Securities Act of 1933, as amended, or under state
securities laws and the resale by you of such Optioned Shares will, therefore,
be restricted. You will be unable to transfer such Optioned Shares without
either registration under such Act and compliance with applicable state
securities laws or the availability of an exemption therefrom. Accordingly, you
represent and warrant to the Company that all shares of Common Stock you may
acquire upon the exercise of this Option will be acquired by you for your own
account for investment and that you will not sell or otherwise dispose of any
such shares except in compliance with all applicable federal and state
securities laws. The Company may place a legend to such effect upon each
certificate representing Optioned Shares acquired by you upon the exercise of
this Option.

            4. Disputes. Any dispute which may arise under or as a result of or
pursuant to this Agreement shall be finally and conclusively determined in good
faith by the Board of Directors of the Company in its sole discretion, and such
determination shall be binding upon all parties.

            5. Termination of Status.

            (a) This Option is a separate incentive and not in lieu of salary or
other compensation. The Optioned Shares do not vest you with any right to
employment with the Company, nor is the Company's right to terminate your
employment in any way restricted by this Agreement. Subject to the following
provisions of this Section 5, the Option will terminate upon and will not be
exercisable after termination of your employment with the Company ("Employment
Termination Date"). If your employment with the Company is terminated for any
reason other than death or disability, this Option may not be exercised after
the earlier of (i) ninety (90) days from the Employment Termination Date or (ii)
the Expiration Date, and may not be exercised for more than the number of
Optioned Shares purchasable under Section 1 on the Employment Termination Date.

            (b) If you die while this Option is exercisable, or within a period
of three months after the Employment Termination Date, the Option may be
exercised by the duly authorized executor of your last will or by the duly
authorized administrator of your estate, but may not be exercised after the
earlier of (i) one year from the date of your death or (ii) the Expiration Date,
and may not be exercised for more than the number of Optioned Shares purchasable
under Section 1 on the date of your death.

            (c) If your employment is terminated as a result of your permanent
disability, this Option may not be exercised after the earlier of (i) one year
from the Employment Termination Date, or (ii) the Expiration Date, and may not
be exercised for more than the number of Optioned Shares purchasable under
Section 1 on the Employment Termination Date. If you die after the date your
employment is terminated under the provisions of this Section 5(c) but before
the Expiration Date, the provisions of Section 5(b) above shall apply.


                                     A - 2
<PAGE>

            Permanent disability shall mean a disability described in Section
422(c)(6) of the Code. The existence of a Disability shall be determined by the
Committee in its absolute discretion.

            6. Adjustments to Exercise Price and Number of Securities. If the
Company shall at any time subdivide or combine the outstanding shares of Common
Stock, or similar corporate events the Exercise Price and the number of shares
subject to the Option shall be appropriately adjusted.

            7. Reservation and Listing of Securities. The Company shall at all
times reserve and keep available out of its authorized shares of Common Stock,
solely for the purpose of issuance upon the exercise of this Option, such number
of shares of Common Stock or other securities, properties or rights as shall be
issuable upon the exercise thereof. The Company covenants and agrees that, upon
exercise of this Option and payment of the Exercise Price therefor, all shares
of Common Stock and other securities issuable upon such exercise shall be duly
and validly issued, fully paid, non-assessable and not subject to the preemptive
rights of any stockholder. As long as this Option shall be outstanding, the
Company shall use its best efforts to cause all shares of Common Stock issuable
upon the exercise of the Option to be listed (subject to official notice of
issuance) on all securities exchanges on which the Common Stock may then be
listed and/or quoted on NASDAQ.

            8. Forfeiture of Option Gains. If at any time within one year after
the exercise of all or any portion of the Option the Committee determines that
the Company has been materially harmed by you, which harm either (a) results in
your being terminated for Cause or (b) results from your engaging in any
activity determined by the Committee, in its sole discretion, to be in
competition with any activity of the Company, or otherwise inimical, contrary or
harmful to the interests of the Company (including, but not limited to,
violating any non-competition or similar agreements entered into with the
Company or otherwise accepting employment with or serving as a consultant,
adviser or in any other capacity to an entity that is in competition with or
acting against the interests of the Company), then upon notice from the Company
to you any gain ("Gain") realized by you upon exercising such Option shall be
paid by you to the Company. For purposes of this Section 8, such Gain shall be
the excess of the Fair Market Value of the shares of Company Stock obtained
through such exercise as of the date of option exercise over the purchase price
of such shares. The Company shall have the right to offset such Gain against any
amounts otherwise owed to you by the Company (including, but not limited to
wages, vacation pay, or pursuant to any benefit plan or other compensatory
arrangement).

            9. Notices.

            All notices, requests, consents and other communications hereunder
shall be in writing and shall be deemed to have been duly made and sent when
delivered, or mailed by registered or certified mail, return receipt requested:

            (a) If to the registered Holder of this Option, to the address of
the Holder as shown on the books of the Company; or


                                     A - 3
<PAGE>

            (b) If to the Company, to 420 Lexington Avenue, Suite 620, New York,
NY 10017, or to such other address as the Company may designate by notice to the
Holders.

            10. Supplements and Amendments. The Company and the Holder may from
time to time supplement or amend this Agreement in any respect, provided,
however, that no amendment may adversely affect your rights hereunder without
your written consent.

            11. Successors. All the covenants and provisions of this Agreement
shall be binding upon and inure to the benefit of the Company, the Holder and
their respective successors and assigns hereunder.

            12. Governing Law. This Agreement shall be deemed to be a contract
made under the laws of the State of New York and for all purposes shall be
construed in accordance with the laws of the State of New York without giving
effect to the rules of the State of New York governing the conflicts of laws.

            13. Entire Agreement; Modification. This Agreement contains the
entire understanding between the parties hereto with respect to the subject
matter hereof.

            14. Severabilitv. If any provision of this Agreement shall be held
to be invalid or unenforceable, such invalidity or unenforceability shall not
affect any other provision of this Agreement.

            15. Captions. The caption headings of the Sections of this Agreement
are for convenience of reference only and are not intended, nor should they be
construed as, a part of this Agreement and shall be given no substantive effect.

            16. Benefits of this Agreement. Nothing in this Agreement shall be
construed to give to any person or corporation other than the Company and the
registered Holder of this Option any legal or equitable right, remedy or claim
under this Agreement; and this Agreement shall be for the sole and exclusive
benefit of the Company and the Holder.

            17. Counterparts. This Agreement may be executed in any number of
counterparts and each of such counterparts shall for all purposes be deemed to
be an original, and such counterparts shall together constitute but one and the
same instrument.

                      [Signature page follows immediately]


                                     A - 4
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be dully executed, as of the day and year first written.

                                        SIGA TECHNOLOGIES, INC.


                                        By: /s/Thomas N. Konatich
                                            ------------------------------------
                                            Name: Thomas N. Konatich
                                            Title: Acting Chief Executive
                                                   Officer, Chief Financial
                                                   Officer and Secretary


                                        /s/ Dennis E. Hruby
                                        ----------------------------------------
                                        Dr. Dennis E. Hruby


                                     A - 5
<PAGE>

                                   Appendix A

                  NOTICE OF INTENTION TO EXERCISE STOCK OPTIONS

The undersigned grantee of a SIGA Technologies, Inc. Stock Option Agreement
dated as of ______________________ to purchase _________ shares of SIGA
Technologies, Inc. common stock hereby gives notice of his or her intention to
exercise the Stock Option (or a portion thereof) and elects to purchase shares
of SIGA Technologies, Inc. common stock.

Shares should be issued in the name of the undersigned and should be sent to the
undersigned at:

________________________________
________________________________
________________________________
________________________________

Dated this _____ day of ________________.

Social Security Number: ________________

Name:  _________________________________


________________________________________
Signature

INSTRUCTIONS: The exercise of these Stock Options is effective on the date the
Company has received all of (1) this Notice of Intention to Exercise Stock
Options, and (2) payment in full in cash of the exercise price for all shares
being purchased pursuant to this Notice.


                                     A - 6