Exhibit 5.1

                        SILVERMAN SCLAR 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

                                                               December 11, 2003

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

Re: Hemispherx Biopharma, Inc. - Registration Statement on Form S-1

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-1, as amended (the "Registration Statement") 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"): (i) 2,050,672 shares (the "Debenture Shares") issuable upon
conversion of the Company's 6% Senior Secured Convertible Debentures due October
2005 (the "Debentures") based upon the conversion price of the Debentures as of
the date hereof, (ii) 410,134 shares (the "Warrant Shares") issuable upon
exercise of certain outstanding warrants of the Company issued on October 29,
2003 to the Debenture holders (the "Warrants"), (iii) 254,846 shares (the
"Interest Shares") issuable as payment of interest on the Debentures, (iv)
950,478 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, (v) 87,500 shares
issuable upon exercise of certain outstanding warrants of the Company issued to
Cardinal Securities LLC and described in the Registrations Statement (the "Other
Warrant Shares") and (vi) 20,682 shares owned in the aggregate by CEOCast, Inc.
and Stephen H. Lieberman (the "Other Shares"). The Debenture Shares, Warrant
Shares, Other Warrant Shares, Other Shares, Interest Shares and Antidilution
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
and Other 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 and Other Warrants in accordance with the Warrants and Other 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,


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fully paid and nonassessable, (iv) the Other Shares to be offered and sold by
the Selling Stockholders have been duly authorized, legally issued, fully paid
and nonassessable, and (v) 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.

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 Shin & Byrne P.C.
                                           -------------------------------------
                                           Silverman Sclar Shin & Byrne P.C.


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