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                                                                       Exhibit 5


                                Bingham Dana LLP
                               150 Federal Street
                                Boston, MA 02110

                                    May 13, 1998

LeukoSite, Inc.
215 First Street
Cambridge, Massachusetts  02142

Dear Sir or Madam:

      We have acted as counsel for LeukoSite, Inc., a Delaware corporation (the
"Company"), in connection with the Company's Registration Statement on Form S-8
to be filed with the Securities and Exchange Commission on May 13, 1998 (the
"Registration Statement").

      The Registration Statement covers the registration of 2,125,000 shares of
common stock, $.01 par value per share, of the Company (the "Shares"), which are
to be issued by the Company upon exercise of employee stock options to be issued
pursuant to the LeukoSite, Inc., Amended and Restated 1993 Stock Option Plan
(the "Plan").

      We have reviewed the corporate proceedings of the Company with respect to
the authorization of the Plan and the issuance of the Shares thereunder. We have
also examined and relied upon originals or copies, certified or otherwise
identified or authenticated to our satisfaction, of such agreements,
instruments, corporate records, certificates, and other documents as we have
deemed necessary or appropriate as a basis for the opinions hereinafter
expressed. In our examination, we have assumed the genuineness of all
signatures, the conformity to the originals of all documents reviewed by us as
copies, the authenticity and completeness of all original documents reviewed by
us in original or copy form, and the legal competence of each individual
executing any document.

      We further assume that all Shares issued upon exercise of options granted
or to be granted pursuant to the Plan will be issued in accordance with the
terms of such Plan and that the purchase price of the Shares will be greater
than or equal to the par value per share of the Shares.

      Subject to the limitations set forth below, we have made such examination
of law as we have deemed necessary for the purposes of this opinion. This
opinion is limited solely to the Delaware General Corporation Law as applied by
courts located in Delaware.

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May 13, 1998
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      Based upon and subject to the foregoing, we are of the opinion that the
Shares, when issued and delivered upon the exercise of options duly granted
pursuant to the Plan and against the payment of the purchase price therefor,
will be validly issued, fully paid, and non-assessable.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.

                                    Very truly yours,


                                    /s/ Bingham Dana LLP
                                    ----------------------------
                                    BINGHAM DANA LLP