Exhibit 5.1
                                                                     -----------

                   [Headed Paper of Osler, Hoskin & Harcourt]







June 9, 2004

Hydrogenics Corporation
5985 McLaughlin Road
Mississauga, Ontario.  L5R 1B8

Dear Sirs:

REGISTRATION STATEMENT ON FORM S-8

         At your request, we have examined the registration statement on Form
S-8 (the "Registration Statement") proposed to be filed pursuant to the United
States Securities Act of 1933, as amended (the "Securities Act"), by Hydrogenics
Corporation, a corporation incorporated under the laws of Canada (the
"Company"), with the United States Securities and Exchange Commission (the
"SEC") on June 9, 2004 relating to the registration under the Securities Act of
an additional 3,500,000 common shares of the Company without par value (the
"Shares") such that up to 8,141,000 Shares shall be for issuance under the
Hydrogenics Stock Option Plan (the "Plan"

EXAMINATIONS.

         In connection with this opinion letter, we have examined the following:
(i) copies of resolutions of the directors of the Company approving the adoption
of the Plan and authorizing the issuance of the Shares (collectively, the
"Resolutions"); and (ii) the proposed form of Registration Statement. We have
also examined the articles of incorporation of the Corporation, its books and
records, such other records and documents provided to us and such statutes,
regulations and other public and corporate records of the Company, and
considered such questions of law as we have considered relevant and necessary
for the purposes of the opinion expressed below.

RELIANCE AND ASSUMPTIONS.

         For the purposes of the opinion expressed below, we have relied upon
the Resolutions and have assumed: (i) the genuineness of all signatures on each
document that we have examined; (ii) the authenticity of all documents submitted
to us as originals, the conformity with the originals of all documents submitted
to us as copies, whether photostatic, telecopied or otherwise; (iii) the legal
power, capacity and authority of all natural persons signing in their individual
capacity; and (iv) that the Resolutions continue to be in force and unamended on
the date hereof.

OPINION.

         Based upon and relying on the foregoing assumptions and subject to the
following qualification and limitation, we are of the opinion that the Shares to
be offered and sold by the Company pursuant to the Registration Statement have
been duly allotted for issuance and, upon the receipt of the consideration
therefor, to the extent required by the terms of the Plan or any other
instruments governing the issuance of the Shares, will be validly issued and
outstanding as fully paid and non-assessable.

QUALIFICATION.

         The foregoing opinion is subject to the qualification that we are
solicitors qualified to practice law solely in the Province of Ontario and we
express no opinion as to any laws or any matters governed by any laws other than
the laws of the Province of Ontario and the federal laws of Canada applicable
therein.

LIMITATION.

         We consent to the use of this opinion as an exhibit to the Registration
Statement and any amendments thereto.



Yours very truly,

/s/ Osler, Hoskin & Harcourt