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                                                                           10.20

                          LEASE MODIFICATION AGREEMENT

      THIS LEASE MODIFICATION AGREEMENT, made this 11th day of January, 2005 by
and between 500 PLAZA DRIVE CORP. having an address c/o Hartz Mountain
Industries, Inc., 400 Plaza Drive, PO Box 1515, Secaucus, New Jersey 07096-1515
(hereinafter referred to as "Landlord") and ALGORX PHARMACEUTICALS, INC. having
an office at 500 Plaza Drive, Secaucus, New Jersey (hereinafter referred to as
"Tenant"). Capitalized terms not otherwise defined herein shall have the
meanings ascribed to such term in the Lease.

                                   WITNESSETH:

      WHEREAS, by Agreement of Lease dated May 10, 2004 (the "Lease") Landlord
leased to Tenant and Tenant hired from Landlord 10,693 square feet of Floor
Space located on the second (2nd)floor of the building located at 500 Plaza
Drive, Secaucus, New Jersey (hereinafter the "Original Demised Premises"); and

      WHEREAS, Landlord and Tenant wish to modify the Lease to reflect an
increase in the area of the Original Demised Premises and amend the Lease
accordingly;

      NOW, THEREFORE, for and in consideration of the Lease, the mutual
covenants herein contained and the consideration set forth herein, the parties
agree as follows:

1.    ADDITIONAL PREMISES: Landlord hereby leases to Tenant, and Tenant hereby
hires from Landlord, subject to the terms, covenants and conditions contained
herein, 5,067 additional square feet of Floor Space located on the second(2nd)
floor of the Building (said 5,067 square feet hereinafter referred to as the
"Additional Premises") commencing on the Additional Premises Commencement Date
and expiring on the Expiration Date of the Lease; said Additional Premises
outlined in red on the Floor Plan attached hereto as Exhibit A and made a part
hereof. Thus the Floor Space of the Additional Premises and the Original Demised
Premises shall equal, in the aggregate, approximately 15,760 square feet.
Effective upon the Additional Premises Commencement Date, except as otherwise
specifically provided herein, all references in the Lease to "Demised Premises"
shall be deemed to include the Additional Premises.

2.    TERM: The "Additional Premises Commencement Date" shall be the earlier of
(a) the date on which both: (i) the Additional Premises shall be Ready for
Occupancy, and (ii) actual possession of the Additional Premises shall have been
delivered to Tenant by notice to Tenant, or (b) the date Tenant, or anyone
claiming under or through Tenant, first occupies the Additional Premises or any
part thereof.

3.    FIXED RENT FOR THE ADDITIONAL PREMISES: Commencing on the Additional
Premises Commencement Date, the Fixed Rent for the Additional Premises shall be
at the annual rate of Twenty Four and 50/100 Dollars ($24.50) multiplied by the
number of square feet of Floor Space of the Additional Premises through the
Expiration Date of the Lease.

4.    PERMITTED USE: Tenant shall use the Additional Premises for the same
Permitted Use

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as set forth in the Lease for the Original Demised Premises.

5.    TENANT'S FRACTION: Effective on the Additional Premises Commencement Date,
Tenant's Fraction shall be modified such that same shall be increased from 2.4%
to 3.54%.

6.    LANDLORD'S WORK: The Additional Premises shall be completed and prepared
for Tenant's occupancy in the manner described in, and subject to the provisions
of, Exhibit B. Tenant shall take possession of the Additional Premises promptly
after the same are Ready for Occupancy and possession thereof is delivered to
Tenant by Landlord giving to Tenant a notice of such effect. Except as expressly
provided to the contrary in this Lease, the taking of possession by Tenant of
the Additional Premises shall be conclusive evidence as against Tenant that the
Additional Premises were in good and satisfactory condition at the time such
possession was taken subject to punch list items, if any (provided, however,
that Tenant provides Landlord with notice of any punch list items within five
(5) days after delivery of possession).

7.    ADDITIONAL LETTER OF CREDIT: As of the date hereof, Tenant shall deposit
with Landlord as a supplement to the security deposit, an additional Letter of
Credit ("Additional Premises Letter of Credit") in the amount of Eighty Seven
Thousand Four Hundred Six and 00/100 Dollars ($87,406.00) (the "Additional
Premises Security Deposit"), which Additional Premises Security Deposit shall be
held by Landlord subject to the terms and provisions of Article 8 of the Lease.
In the event Landlord shall be entitled to draw down on the Letter of Credit (as
defined in Article 8 of the Lease) pursuant to Article 8, Landlord shall have a
corresponding right to draw down on the Additional Premises Letter of Credit,
and may draw upon either or both in such circumstance, subject to the provisions
of said Article 8.

      IN WITNESS WHEREOF, the parties hereto have caused this Lease Modification
Agreement to be duly executed as of the day and year first above written.

                                                               ("LANDLORD")
                                               500 PLAZA DRIVE CORP.

                                          By:  /s/ Irwin A. Horowitz
                                               -------------------------
                                               Irwin A. Horowitz
                                               Executive Vice President

                                                      ("TENANT")
                                               ALGORX PHARMACEUTICALS, INC.

                                          By:  /s/ Jeffrey Rona
                                               --------------------------
                                               Name:   Jeffrey Rona
                                               Title: CFO

                                       2
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                                                                       EXHIBIT B

                              LANDLORDS WORKLETTER

                             ALGORX PHAMACEUTICALS

                                 500 PLAZA DRIVE
                                  SECAUCUS, NJ

      1.    Existing acoustical ceiling grid and tile, and light fixtures shall
            remain in office expansion area except where damaged by the removal
            of walls.

      2     Provide new floor and wall finishes to match existing office area
            finishes.

      3.    Provide new doors and frames to match existing office area doors.