Exhibit 5.1

                     SILVERMAN SCLAR BYRNE SHIN & BYRNE P.C.
                        381 Park Avenue South, Suite 1601
                            New York, New York 10016
                              Tel. No. 212-779-8600

                        Telecopy Number - (212) 779-8858

                                  May 20, 2003

Board of Directors
Hemispherx Biopharma, Inc.
1617 JFK Boulevard
Philadelphia, PA 19103

Re: Hemispherx Biopharma, Inc. - Registration Statement on Form S-3

Gentlemen:

We have acted as counsel for Hemispherx Biopharma, Inc., a Delaware corporation
(the "Company"), in connection with the preparation of the registration
statement on Form S-3 relating to the registration under the Securities Act of
1933, as amended (the "Act"), of the following shares of the Company's Common
Stock, par value $0.001 per share (the "Common Stock"): 3,716,438 shares (the
"Debenture Shares") issuable upon conversion of the Company's 6% Senior Secured
Convertible Debentures due 2005 (the "Debentures") based upon the conversion
price of the Debentures as of the date hereof, 743,288 shares (the "Warrant
Shares") issuable upon exercise of certain outstanding warrants of the Company
issued on March 12, 2003 (the "Warrants"), 446,287 shares (the "Interest
Shares") issuable as payment of interest on the Debentures, 1,717,105 shares
(the "Antidilution Shares") issuable upon conversion of the Debentures or
exercise of the Warrants as a result of adjustments to the conversion price of
the Debentures or the exercise price of the Warrants, as the case may be, in
accordance with the respective terms thereof, 487,028 shares issued to
Interferon Sciences, Inc. (the "ISI Shares") and 347,445 shares issued to
Provesan SA (the "Provesan Shares"). The Debenture Shares, Warrant Shares,
Interest Shares, Antidilution Shares, ISI Shares and Provesan Shares are to be
offered and sold by certain securityholders of the Company (the "Selling
Stockholders").

We have reviewed and are familiar with such corporate proceedings and other
matters as we have deemed necessary for this opinion. Based upon the foregoing,
we are of the opinion that (i) the Debenture Shares to be offered and sold by
the Selling Stockholders have been duly authorized and, when issued by the
Company upon conversion of the Debentures in accordance with the Debentures,
will be legally issued, fully paid and nonassessable, (ii) the Warrant Shares to
be offered and sold by the Selling Stockholders





have been duly authorized and, when issued by the Company upon exercise of the
Warrants in accordance with the Warrants, will be legally issued, fully paid and
nonassessable, (iii) the Interest Shares to be offered and sold by the Selling
Stockholders have been duly authorized and, when issued by the Company as
payment of interest on the Debentures in accordance with the Debenture, will be
legally issued, fully paid and nonassessable, (iv) the Antidilution Shares to be
offered and sold by the Selling Stockholders have been duly authorized and, when
issued by the Company upon conversion of the Debentures in accordance with the
Debenture or upon exercise of the Warrants in accordance with the Warrants, as
the case may be, will be legally issued, fully paid and nonassessable, (v) the
ISI Shares to be offered and sold by the Selling Stockholders have been duly
authorized, and are legally issued, fully paid and nonassessable, and (vi) the
Provesan Shares to be offered and sold by the Selling Stockholders have been
duly authorized, and are legally issued, fully paid and nonassessable.

This opinion is limited to matters governed by the General Corporation Law of
the State of Delaware. No opinion is expressed as to the effect that the law of
any other jurisdiction may have upon the subject matter of the opinion expressed
herein under conflicts of law principles, rules and regulations or otherwise.

This opinion is limited to the specific issues addressed herein, and no opinion
may be inferred or implied beyond that expressly stated herein. We assume no
obligation to revise or supplement this opinion should the present laws of the
State of Delaware be changed by legislative action, judicial decision or
otherwise.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the Registration Statement and in the Prospectus included therein.
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 or the rules and
regulations of the Securities and Exchange Commission promulgated thereunder.

This opinion is furnished to you in connection with the filing of the
Registration Statement and is not to be used, circulated, quoted or otherwise
relied upon for any other purposes.

                                     Very truly yours,

                                     s/ Silverman Sclar Byrne Shin & Byrne P.C.

                                     Silverman Sclar Byrne Shin & Byrne P.C.