AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 9, 1997
                                           REGISTRATION STATEMENT NO. 333-
 
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                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549
                                ---------------
                                   FORM SB-2
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
                                ---------------
                          SIGA PHARMACEUTICALS, INC.
                (NAME OF SMALL BUSINESS ISSUER IN ITS CHARTER)
 
         DELAWARE                    2834                    13-3864870
     (STATE OR OTHER     (PRIMARY STANDARD INDUSTRIAL     (I.R.S. EMPLOYER    
     JURISDICTION OF      CLASSIFICATION CODE NUMBER)     IDENTIFICATION NO.) 
     INCORPORATION OR                           
      ORGANIZATION)
                                --------------- 

                               666 THIRD AVENUE
                              NEW YORK, NY 10017
                                (212) 681-4970
                 (ADDRESS AND TELEPHONE NUMBER OF PRINCIPAL 
              EXECUTIVE OFFICES AND PRINCIPAL PLACE OF BUSINESS)
                                ---------------
           DAVID H. DE WEESE, PRESIDENT AND CHIEF EXECUTIVE OFFICER
                          SIGA PHARMACEUTICALS, INC.
                               666 THIRD AVENUE
                              NEW YORK, NY 10017
                                (212) 681-4970
           (NAME, ADDRESS AND TELEPHONE NUMBER OF AGENT FOR SERVICE)
                                ---------------
                                  COPIES TO:
         ADAM EILENBERG, ESQ.                    KENNETH KOCH, ESQ.
          EILENBERG & ZIVIAN                 SQUADRON, ELLENOFF, PLESENT
           666 THIRD AVENUE                       & SHEINFELD, LLP
          NEW YORK, NY 10017                      551 FIFTH AVENUE
            (212) 986-2468                       NEW YORK, NY 10176
       FACSIMILE (212) 986-2399                    (212) 476-8362
                                              FACSIMILE (212) 697-6686
 
  APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: As soon as
practicable after this Registration Statement becomes effective. If any of the
securities being registered on this Form are to be offered on a delayed or
continuous basis pursuant to Rule 415 under the Securities Act of 1933, check
the following box: [X]
 
  If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, check the following box and
list the Securities Act registration statement number of earlier effective
registration statement for the same offering. [X] File No. 333-23037
 
  If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [_]
 
  If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [_]
                                ---------------
                        CALCULATION OF REGISTRATION FEE
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PROPOSED PROPOSED MAXIMUM TITLE OF EACH CLASS AMOUNT MAXIMUM AGGREGATE OF SECURITIES TO BE TO BE OFFERING PRICE OFFERING AMOUNT OF REGISTERED REGISTERED PER SHARE(1) PRICE(1) REGISTRATION FEE - ------------------------------------------------------------------------------- Common Stock, par value $.0001(2)............. 287,500 $ 5.00 $1,437,500 $436 - ------------------------------------------------------------------------------- Representatives' Warrants, each to purchase one share of Common Stock(3)....... 25,000 $0.001 $25 -- (4) - ------------------------------------------------------------------------------- Common Stock, par value $.0001(5)(6).......... 25,000 $8.25 $206,250 $ 63 - ------------------------------------------------------------------------------- Total: ................ $1,643,775 $499
- ------------------------------------------------------------------------------- - ------------------------------------------------------------------------------- (1) Estimated solely for the purpose of calculating the registration fee. (2) Includes an aggregate 37,500 Common Stock to cover over-allotments, if any, pursuant to an over-allotment option granted to the Underwriters. (3) To be issued to the Representatives at the time of delivery and acceptance of the securities to be sold to the public hereunder. (4) No fee due pursuant to Rule 457(g) under the Securities Act of 1933. (5) Issuable upon exercise of the Representatives' Warrants. (6) Also registered hereunder pursuant to Rule 416 are an indeterminate number of shares of Common Stock which may be issued pursuant to the anti- dilution provisions applicable to the Representatives' Warrants. --------------- THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(a), MAY DETERMINE. - ------------------------------------------------------------------------------- - ------------------------------------------------------------------------------- INCORPORATION BY REFERENCE OF REGISTRATION STATEMENT ON FORM SB-2, FILE NO. 333-23037 SIGA Pharmaceuticals, Inc. (the "Company") hereby incorporates by reference into this Registration Statement on Form SB-2 in its entirety the Registration Statement on Form SB-2 (File No. 333-23037 ) declared effective on September 9, 1997 by the Securities and Exchange Commission (the "Commission"), including each of the documents filed by the Company with the Commission and incorporated or deemed to be incorporated by reference therein. EXHIBITS Exhibit Number Description - ---------- ------------------------------------------------------------ 5(a)* Opinion of Eilenberg & Zivian. 24(a)* Consent of Eilenberg & Zivian (included in Exhibit 5(a). 24(b)* Consent of Price Waterhouse LLP *Filed herewith. SIGNATURES IN ACCORDANCE WITH THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE UNDERSIGNED REGISTRANT CERTIFIES THAT IT HAS REASONABLE GROUNDS TO BELIEVE THAT IT MEETS ALL OF THE REQUIREMENTS FOR FILING ON FORM SB-2 AND AUTHORIZED THIS REGISTRATION STATEMENT TO BE SIGNED ON ITS BEHALF BY THE UNDERSIGNED, THEREUNTO DULY AUTHORIZED, IN THE CITY OF NEW YORK, ON THE 9TH DAY OF SEPTEMBER, 1997. SIGA Pharmaceuticals, Inc. /s/ David H. de Weese By: _________________________________ David H. de Weese Chairman, President, Chief Executive Officer and Director (Principal Executive Officer) IN ACCORDANCE WITH THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS REGISTRATION STATEMENT OR AMENDMENT HAS BEEN SIGNED BELOW BY THE FOLLOWING PERSONS IN THE CAPACITIES AND ON THE DATES INDICATED:
SIGNATURE TITLE DATE --------- ----- ---- /s/ Joshua D. Schein Chief Financial Officer September 9, 1997 ____________________________________ (Principal Accounting and Dr. Joshua D. Schein Financial Officer), Executive Vice President, Secretary and Director /s/ Judson A. Cooper Executive Vice President and September 9, 1997 ____________________________________ Director Judson A. Cooper /s/ Terence E. Downer Director September 9, 1997 ____________________________________ Terence E. Downer

 
                                                                    EXHIBIT 5(a)



                               Eilenberg & Zivian
                          666 Third Avenue, 30th Floor
                               New York, NY 10017


                                                September 9, 1997

SIGA Pharmaceuticals, Inc.
666 Third Avenue, 30th Floor
New York, NY 10017


Ladies and Gentlemen:

    You have requested our opinion, as counsel for SIGA Pharmaceuticals, Inc., a
Delaware corporation (the "Company"), in connection with the registration
statement on Form SB-2 (the "Abbreviated Registration Statement"), under the
Securities Act of 1933, as amended (the "Act"), for the registration of 287,500
shares (including up to 37,500 shares exercisable upon exercise of the
Underwriters' Over-Allotment Option) of common stock, par value $.0001 per
share, of the Company (the "Common Stock"), 25,000 Representatives' Warrants and
up to 25,000 shares of the Company's Common Stock issuable upon exercise of the
Representatives' Warrants.  The Abbreviated Registration Statement relates to
the same class of securities registered pursuant to the Company's Registration
Statement on Form SB-2 (No. 333-23037) declared effective earlier today (the
"Initial Registration Statement").

    The Abbreviated Registration Statement, together with the Initial
Registration Statement, relates to an offering by the Company of 2,500,000
shares (or, upon the exercise of the Underwriters' Over-Allotment Option, up to
375,000 additional shares) of Common Stock.

    We have examined such records and documents and made such examinations of
law as we have deemed relevant in connection with this opinion.  It is our
opinion that when there has been compliance with the Act and the applicable
state securities laws, the shares of Common Stock to be sold by the Company,
when issued, delivered, and paid for in the manner described in the form of
Underwriting Agreement filed as Exhibit 1(a) to the Initial Registration
Statement will be legally issued, fully paid and nonassessable.

    We hereby consent to the filing of this opinion as an exhibit to the
Abbreviated Registration Statement and to the reference to our firm under the
caption "Legal Matters" in the Initial Registration Statement.  In so doing, we
do not admit that we are in the category of persons whose consent is required
under Section 7 of the Act or the rules and regulations of the Securities and
Exchange Commission promulgated thereunder.


                                Very truly yours,

 

                                /s/ Eilenberg & Zivian
                                ----------------------
                                Eilenberg & Zivian

 
                                                                   EXHIBIT 24(b)

                      CONSENT OF INDEPENDENT ACCOUNTANTS

We hereby consent to the use in the Prospectus constituting part of this 
Registration Statement on Form SB-2 of our report dated March 3, 1997 relating 
to the financial statements of SIGA Pharmaceuticals, Inc., which appears in such
Prospectus.  We also consent to the reference to us under the heading "Experts"
in such Prospectus.

PRICE WATERHOUSE LLP
New York, New York
September 9, 1997