Exhibit 5.1

November 21, 2007


MacroChem Corporation
40 Washington Street, Suite 220
Wellesley Hills, MA 02481

Re:   Registration Statement on Form S-1


Ladies and Gentlemen:


     This opinion is furnished to you in connection with a registration
statement on Form S-1 (the 'Registration Statement'), filed today with the
Securities and Exchange Commission under the Securities Act of 1933, as amended,
for the registration of shares of Common Stock, $.01 par value (the 'Common
Stock'), of MacroChem Corporation, a Delaware corporation (the 'Company'),
comprised of (i) 5,891,666 shares of Common Stock (the 'Issued Shares') and (ii)
13,984,044 shares of Common Stock (the 'Warrant Shares') issuable upon the
exercise of warrants (the 'Warrants'). The Issued Shares and the Warrant Shares
are referred to collectively herein as the 'Registrable Securities.'


Please be advised that as counsel to the Company, upon examination of such
corporate documents and records as we have deemed necessary or advisable for the
purposes of this opinion, it is our opinion that the Registrable Securities
included in the Registration Statement are duly authorized and that they are or
will be upon issuance in accordance with their applicable documents and
instruments, legally and validly issued, fully paid and nonassessable.


We have assumed that no issuance of the Warrant Shares will result in the
issuance by the Company of shares in excess of its authorized Common Stock and
that the price received by the Company for the Warrant Shares issued upon
exercise of the Warrants will not be less than the par value thereof.

We understand the Registrable Securities are being registered to permit the
resale of such Common Stock by the holders thereof from time to time after the
effective date of the Registration Statement.

The remaining shares covered by the Prospectus filed today with Registration
Statement were originally registered on the Form S-1 filed with the Securities
and Exchange Commission on March 30, 2006, which was declared effective on April
18, 2006 and subsequently amended by post-effective amendment on April 30, 2007
(the 'Prior Registration Statement'). Upon being declared effective, the
Registration Statement will act as a post-effective amendment to the Prior
Registration Statement.

We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement, and to the reference to our firm under the hearing
'Legal Matters' in the prospectus comprising a part of the Registration
Statement.

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 General Corporation
Law of the State of Delaware.

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

Very truly yours,

/s/ Ropes & Gray LLP

Ropes & Gray LLP