EXHIBIT 5

                            [ROPES & GRAY LETTERHEAD]


                                  May 21, 2002

Boston Life Sciences, Inc.
137 Newbury Street
Boston, Massachusetts 02116

         Re:   Boston Life Sciences, Inc.

Ladies and Gentlemen:

         This opinion is furnished to you in connection with a registration
statement on Form S-3 (the "Registration Statement"), filed today with the
Securities and Exchange Commission under the Securities Act of 1933, as amended,
for the registration of (i) 1,599,568 shares of Common Stock, $.01 par value
(the "Shares"), of Boston Life Sciences, Inc., a Delaware corporation (the
"Company"), (ii) 573,205 shares of the Company's Common Stock issuable upon the
exercise of certain warrants (the "Private Placement Warrants"), (iii) 160,000
shares of the Company's Common Stock issuable upon the exercise of Warrant No.
BLSI-J-155 (the "Pictet Warrants"), (iv) 10,000 shares of the Company's Common
Stock issuable upon the exercise of Warrant No. BLSI-2002-25 (the "Licho
Warrants"), and (v) 25,000 shares of the Company's Common Stock issuable upon
the exercise of Warrant No. BLSI-2002-30 (the "Alexandros Warrants").

         The Common Stock issuable upon exercise of the Private Placement
Warrants, Pictet Warrants, Licho Warrants, and Alexandros Warrants is referred
to herein as the "Private Placement Warrant Shares," "Pictet Warrant Shares,"
"Licho Warrant Shares," and "Alexandros Warrant Shares" respectively. The
Private Placement Warrant Shares, Pictet Warrant Shares, Licho Warrant Shares,
and Alexandros Warrant Shares, together with the Shares, are referred to as the
"Registrable Shares."

         The Company originally sold the Shares and 399,892 of the Private
Placement Warrants pursuant to Subscription Agreements dated March 12, 2002
between the Company and each investor in the private placement (the
"Subscription Agreements"). The Company also issued 157,557 and 15,756 Private
Placement Warrants to Brimberg & Co., L.P. and Celia Kupferberg, respectively,
in connection with the private placement. The Company issued the Pictet Warrants
pursuant to an agreement between the Company and Pictet Global Sector
Fund-Biotech in June 2001 (the "Pictet Agreement"). The Company issued the Licho
Warrants pursuant to a consulting agreement between the Company and Robert Licho
dated as of October 1, 2001 (the "Licho Agreement"). The Company issued the
Alexandros Warrants pursuant to a consulting agreement between the Company and
Alexandros Partners LLC dated as of April 1, 2002 (the "Alexandros Agreement").
The Registrable Shares are being registered to permit the secondary trading of
such Common Stock by the holders thereof from time to time after the effective
date of the Registration Statement.

         We have acted as counsel for the Company in connection with its
issuance and sale of the Shares and the Private Placement Warrants and the
preparation of the Subscription Agreements. We have also acted as counsel for
the Company in connection with its issuance of the Pictet Warrants. We have not
acted as counsel for the Company in connection with its issuance of the Licho
Warrants or the Alexandros Warrants or the preparation of the Licho Agreement or
the




Alexandros Agreement. For purposes of this opinion, we have examined and relied
upon such documents, records, certificates and other instruments as we have
deemed necessary.

       We express no opinion as to the applicability of, compliance with or
effect of Federal law or the law of any jurisdiction other than The Commonwealth
of Massachusetts and the corporate laws of the State of Delaware.

       Based on the foregoing, we are of the opinion that the Registrable Shares
have been duly authorized and:

1.   When the Shares were issued, the Shares were validly issued, fully paid and
     non-assessable.

2.   When the Private Placement Warrant Shares are issued out of the Company's
     duly authorized Common Stock upon exercise of, and pursuant to the
     provisions of, the Private Placement Warrants and the Subscription
     Agreements and the Company has received the consideration therefor in
     accordance with the terms of the Private Placement Warrants and the
     Subscription Agreements, the Private Placement Warrant Shares will be
     validly issued, fully paid and non-assessable.

3.   When the Pictet Warrant Shares are issued out of the Company's duly
     authorized Common Stock upon exercise of, and pursuant to the provisions
     of, the Pictet Warrants and the Pictet Agreement and the Company has
     received the consideration therefor in accordance with the terms of the
     Pictet Warrants and the Pictet Agreement, the Pictet Warrant Shares will be
     validly issued, fully paid and non-assessable.

4.   When the Licho Warrant Shares are issued out of the Company's duly
     authorized Common Stock upon exercise of, and pursuant to the provisions
     of, the Licho Warrants and the Licho Agreement and the Company has received
     the consideration therefor in accordance with the terms of the Licho
     Warrants and the Licho Agreement, the Licho Warrant Shares will be validly
     issued, fully paid and non-assessable.

5.   When the Alexandros Warrant Shares are issued out of the Company's duly
     authorized Common Stock upon exercise of, and pursuant to the provisions
     of, the Alexandros Warrants and the Alexandros Agreement and the Company
     has received the consideration therefor in accordance with the terms of the
     Alexandros Warrants and the Alexandros Agreement, the Alexandros Warrant
     Shares will be validly issued, fully paid and non-assessable.

       We hereby consent to your filing this opinion as an exhibit to the
Registration Statement and to the use of our name therein and in the related
prospectus under the caption "Legal Matters".



     It is understood that this opinion is to be used only in connection with
the offer and sale of the Shares while the Registration Statement is in effect.

                                     Very truly yours,

                                     /s/ Ropes & Gray
                                     -------------------

                                     Ropes & Gray