EXHIBIT 4.1

         NUMBER                                                 SHARES

                                 LeukoSite Inc.

              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE
                                             SEE REVERSE FOR CERTAIN DEFINITIONS
                                                               CUSIP 52728R 10 2

       THIS CERTIFIES THAT            SPECIMEN




       is the owner of   XXXX

       FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK, $.01 PAR VALUE, OF

                                 LeukoSite, Inc.

(hereinafter called the Corporation, transferable on the books of the
Corporation by the holder hereof, in person or by duly authorized attorney, upon
surrender of this Certificate properly endorsed or accompanied by a proper
assignment. This Certificate and the shares represented by this Certificate are
issued and shall be subject to the laws of the State of Delaware and to the
provisions of the Certificate of Incorporation and the By-Laws of the
Corporation as amended from time to time (copies of which are on file at the
principal office of the Corporation and the Transfer Agent), to all of which the
holder of this Certificate by acceptance hereof assents.

This Certificate is not valid until countersigned by the Transfer Agent and
registered by the Registrar.

IN WITNESS WHEREOF, the Corporation has caused the facsimile signatures of its
duly authorized officers and its facsimile seal to be hereunto affixed.

Dated:

                                 LEUKOSITE, INC.
                                      1992
                                    DELAWARE

                  TREASURER                         PRESIDENT





                                 LeukoSite, Inc.

The Corporation is authorized to issue more than one class of stock. Upon
written request the Corporation will furnish without charge to each stockholder
a copy of the powers, designations, preferences and relative, participating,
optional or other special rights of each class of stock or series thereof and
the qualifications, limitations or restrictions of such preferences and/or
rights.

THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE OFFERED, SOLD, ASSIGNED,
PLEDGED, TRANSFERRED OR OTHERWISE DISPOSED OF EXCEPT (I) PURSUANT TO AN
EFFECTIVE REGISTRATION STATEMENT UNDER SAID ACT, (II) PURSUANT TO AN AVAILABLE
EXEMPTION FROM REGISTRATION UNDER SAID ACT AND, IF REQUESTED, BY THE COMPANY,
UPON DELIVERY OF AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY
THAT THE PROPOSED TRANSFER IS EXEMPT FROM SAID ACT OR (III) PURSUANT TO THE
RESALE PROVISIONS OF RULE 144.

The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

TEN COM - as tenants in common                UNIF GIFT MIN ACT _____ Custodian
TEN ENT - as tenants by the entireties         under Uniform Gift to Minors Act
JT TEN - as joint tenants with right of survivorship
and not as tenants in common
COM PROP - as community property


     Additional abbreviations may also be used though not in the above list.


For value received ________hereby sell, assign and transfer unto

Please insert social security or other identifying number of assignee

(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)

Shares of the common stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint _____Attorney to transfer the said stock on
the books of the within-named Corporation with full power of substitution in the
premises.

Dated:

NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS
WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR WITHOUT ALTERATION
OR ENLARGEMENT OR ANY CHANGE WHATEVER.

Signature(s) Guaranteed

THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GRANTOR INSTITUTION (BANKS,
STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN
AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM), PURSUANT TO SEC RULE
17Ad-15.