Exhibit 5.1

                    AKIN, GUMP, STRAUSS, HAUER & FELD, L.L.P.
                                ATTORNEYS AT LAW

AUSTIN               A REGISTERED LIMITED LIABILITY PARTNERSHIP
BRUSSELS                INCLUDING PROFESSIONAL CORPORATIONS
DALLAS
HOUSTON                          590 MADISON AVENUE
LONDON                               20TH FLOOR
LOS ANGELES                      NEW YORK, NY 10022
MOSCOW                             (212) 872-1000
NEW YORK                         FAX (212) 872-1002
PHILADELPHIA
SAN ANTONIO
WASHINGTON, D.C.                  October 31, 2001

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549

      Re: SIGA Technologies, Inc. Form S-3

Ladies and Gentlemen:

      We have acted as special counsel to SIGA Technologies, Inc., a Delaware
corporation (the "Company"), in connection with the registration statement on
Form S-3 (the "Registration Statement"), filed with the Securities and Exchange
Commission (the "SEC") under the Securities Act of 1933, as amended (the "Act"),
covering the offering and sale by the selling stockholders listed in the
Registration Statement (the "Selling Stockholders") of 716,862 shares (the
"Selling Stockholder Shares") of the Company's Common Stock, par value $0.0001
per share.

      We have examined originals or certified copies of such corporate records
of the Company and other certificates and documents of officials of the Company,
public officials and others as we have deemed appropriate for purposes of this
letter. We have assumed the genuineness of all signatures, the authenticity of
all documents submitted to us as originals, the conformity to authentic original
documents of all copies submitted to us as conformed and certified or reproduced
copies.

      Based upon the foregoing and subject to the assumptions, exceptions,
qualifications and limitations set forth hereinafter, we are of the opinion that
when the Registration Statement relating to the Selling Stockholder Shares has
become effective under the Act, the Selling Stockholder Shares, when sold and
delivered as described in the Registration Statement, will be duly authorized
and validly issued and are fully paid and non-assessable.


October 31, 2001
Page 2

      The opinions and other matters set forth in this letter are qualified in
their entirety and subject to the following:

      A.    We express no opinion as to the laws of any jurisdiction other than
            any published constitutions, treaties, laws, rules or regulations or
            judicial or administrative decisions ("Laws") of the Laws of the
            state of Delaware.

      B.    This law firm is a registered limited liability partnership
            organized under the laws of the State of Texas.

      C.    This opinion is limited to the matters stated herein, and no opinion
            is implied or may be inferred beyond the matters expressly stated.
            We assume herein no obligation, and hereby disclaim any obligation,
            to make any inquiry after the date hereof or to advise you of any
            future changes in the foregoing or of any fact or circumstance that
            may hereafter come to our attention.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of our name in the prospectus forming a
part of the Registration Statement under the caption "Legal Matters." In giving
this consent, we do not thereby admit that we are within the category of persons
whose consent is required under Section 7 of the Act, and the rules and
regulations promulgated thereunder. We also consent to the filing of copies of
this opinion as an exhibit to the Registration Statement.

                                       Very truly yours,


                                       AKIN, GUMP, STRAUSS, HAUER & FELD, L.L.P.