February 2, 1999

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

      Re:   Registration Statement on Form S-3

Gentlemen:

      We have acted as counsel to  Hemispherx  Biopharma,  Inc.  ("Company"),  a
Delaware corporation,  pursuant to Registration  Statement on Form S-3, as filed
with the Securities and Exchange  Commission on December 8, 1998  ("Registration
Statement"),  covering (i) 750,000 shares of the Company's  common stock,  $.001
par value ("Common  Stock");  and (ii) 250,000 shares of Common Stock underlying
warrants.

      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.


Hemispherx Biopharma, Inc.
February 2, 1999
Page 2


            2. The Common Stock has been duly  authorized and is validly issued,
fully paid and  non-assessable.  The Common Stock  underlying  the warrants have
been duly authorized and when issued,  delivered and paid for in accordance with
the   warrants'   terms  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 thereto, or the effect thereon,
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 in  connection  with the
Registration  Statement.  It is not to be used, circulated,  quoted or otherwise
referred to for any other purpose.

                                Very truly yours,

                                SILVERMAN, COLLURA, CHERNIS
                                     & BALZANO, P.C.

                                /s/ SILVERMAN, COLLURA, CHERNIS & BALZANO, P.C.