Exhibit 5.1

               [LETTERHEAD OF SILVERMAN, COLLURA & CHERNIS, P.C.]

                                                              March 15, 2001

Hemispherx Biopharma, Inc.
1617 JFK Boulevard
Philadelphia, Pennsylvania 19103.

                  Re: Registration Statement on Form S-8

Gentlemen:

      We have acted as counsel to Hemispherx Biopharma,  Inc. (the "Company"), a
Delaware corporation, pursuant to a Registration Statement on Form S-8, as filed
with the Securities and Exchange Commission on March 16, 2001 (the "Registration
Statement"),  covering an aggregate of 691,198  shares of the  Company's  Common
Stock,  $.001 par value (the "Common Stock") issuable  pursuant to the Company's
1990, 1992 and 1993 Employee Stock Purchase Plans.

      In acting as counsel  for the  Company  and  arriving  at the  opinions as
expressed below, we have examined and relied upon originals or copies, certified
or otherwise  identified  to our  satisfaction,  of such records of the Company,
agreements and other instruments,  certificates of officers and  representatives
of the Company,  certificates of public officials and other documents as we have
deemed necessary or appropriate as a basis for the opinions expressed herein.

      In connection  with our examination we have assumed the genuineness of all
signatures,  the authenticity of all documents tendered to us as originals,  the
legal capacity of natural  persons and the  conformity to original  documents of
all documents submitted to us as certified or photostated copies.

      Based on the foregoing,  and subject to the qualifications and limitations
set forth herein, it is our opinion that:

      1. The Company has  authority  to issue the Common Stock in the manner and
under the terms set forth in the Registration Statement.



      2. The Common Stock has been duly  authorized  and when issued,  delivered
and paid for by recipients in accordance with their  respective  terms,  will be
validly issued, fully paid and non-assessable.

      We  express no  opinion  with  respect to the laws other than those of the
State of New York and  Federal  Laws of the  United  States of  America,  and we
assume no  responsibility  as to the  applicability or the effect of the laws of
any other jurisdiction.

      We hereby  consent  to the filing of this  opinion  as Exhibit  5.1 to the
Registration Statement and its use as part of the Registration Statement.

      We are  furnishing  this opinion to the Company  solely for its benefit in
connection with the Registration  Statement.  It is not to be used,  circulated,
quoted or otherwise referred to for any other purpose. Other than the Company no
one is entitled to rely on this opinion.

                                      Very truly yours,

                                      SILVERMAN, COLLURA & CHERNIS, P.C.