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                                                                   EXHIBIT 10.18

                             FOURTH LEASE AMENDMENT

                          NORTHFIELD LABORATORIES INC.
               1200 BUSINESS CENTER DRIVE, MT. PROSPECT, ILLINOIS

         This Fourth Lease Amendment to Lease (the "Amendment") is made as of
this, 22nd day of September 2003, by and between First Industrial, L.P., a
Delaware Limited Partnership, ("Landlord" or "Lessor") and Northfield
Laboratories Inc., ("Tenant" or "Lessee").

                                   WITNESSETH

         WHEREAS, Landlord and Tenant entered into that certain lease (the
"Lease"), dated June 8, 1989 demising approximately 20,400 square feet (the
"Premises") of the building (the "Building") located at 1200 Business Center
Drive, Mount Prospect, Illinois; and

         WHEREAS, Lessor and Lessee entered into that First Lease Amendment (the
"First Lease Amendment"), dated November 24, 1992 redefining the term; and

         WHEREAS, Lessor and Lessee entered into that Second Lease Amendment
(the "Second Lease Amendment"), dated May 6, 1998 Lessee exercises it's second
option to renew, and

         WHEREAS, Lessor and Lessee entered into that Third Lease Amendment (the
"Third Lease Amendment"), dated September 16th, 1999 expanding the premises and
establishing a term, and

         NOW, THEREFORE, in consideration of the foregoing recitals, and for
other good and valuable consideration, the receipt and legal sufficiency of
which are hereby acknowledged, Landlord and tenant agree as follows:

         1.   Definition. For all purposes of this Amendment, any capitalized
              terms utilized, but not defined, in this Amendment shall have the
              same meanings as are ascribed to such terms in the Lease.

         2.   Extension of the Lease Term. Effective as of September 1, 2004,
              the term of the Lease (the "Term") is hereby extended for a
              five-year period (the "Extended Term"). During the Extended Term,
              all of the conditions set forth in the original Lease shall remain
              in full force and effect, except as expressly modified by or
              inconsistent with, the terms of this Amendment.

         3.   Rent. The monthly base rent schedule shall be amended as follows:

              September 1, 2004 through August 30, 2006.....$23,492.60 per month

              September 1, 2006 through August 30, 2009.....$23,957.80 per month

         4.   Extension. Lessee shall have three (3) additional five-year
              options under the same term and conditions as Article XXIV of the
              First Lease Amendment.

         5.   Conflict. In the event there is conflict or inconsistency between
              the term and condition of this Amendment and the terms and
              conditions of the Lease, the terms and conditions of this
              Amendment shall control.

         6.   All other terms and conditions of the original Lease will remain
              in full force and effect.

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         IN WITNESS WHEREOF, Landlord and Tenant have executed this Amendment as
         of the date first written above.

                                            LANDLORD/LESSOR
                                            FIRST INDUSTRIAL, L.P.,
                                            a Delaware limited partnership

                                            By:   /s/ First Industrial
                                                --------------------------------
                                                  First Industrial
                                            Its:  Regional Director

                                            LESSEE/TENANT:
                                            NORTHFIELD LABORATORIES INC.

                                            By:   /s/ Jack Kogut
                                                --------------------------------
                                                  Jack Kogut
                                                  Sr. Vice President<PAGE>
                                                                   EXHIBIT 10.44

                                    AMENDMENT

                                       TO

                            STOCK PURCHASE AGREEMENT

         This Amendment, dated as of October 1, 2003, amends the Stock Purchase
Agreement (the "Agreement"), dated as of October 22, 2001, by and between (i)
SPSS Inc., a Delaware corporation (the "SPSS"), and (ii) America Online, Inc., a
Delaware corporation ("Buyer"). Capitalized terms used herein but not otherwise
defined herein have the meanings attributed to such terms in the Agreement.

         In consideration of the mutual covenants set forth herein, and other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree to amend the Agreement as follows:

         1. Amendments to Section 1. The parties hereby acknowledge that SPSS
has issued to Buyer 158,228 shares of Common Stock pursuant to Section 1(b)(i)
of the Agreement and 291,828 additional shares of Common Stock pursuant to
Section 1(b)(ii) of the Agreement. Section 1 of the Agreement is hereby amended
to terminate any further obligations of the parties thereunder, including
without limitation any obligation of SPSS to issue any additional shares of
Common Stock to Buyer on the second or third anniversary of the Effective Date,
any obligation of SPSS to issue any additional shares of Common Stock to Buyer
based on the closing price of such Common Stock on any Subsequent Preceding
Date, and Buyer's obligation to deliver to SPSS cash or shares of Common Stock
based on the closing price of such Common Stock on any Subsequent Preceding
Date.

         2. Amendment to Section 4. Section 4 of the Agreement is hereby amended
to terminate the parties obligations under subsection (a), (d) and (e) thereof.

         3. Amendment to Section 5. Section 5 of the Agreement is deleted in its
entirety and replaced with the following:

                  "5. REPORTS AND COOPERATION.

                           (a) REPORTS UNDER THE EXCHANGE ACT. With a view to
making available to Buyer the benefits of Commission Rule 144 promulgated under
the 1933 Act and any other rule or regulation of the Commission that may at any
time permit Buyer to sell securities of SPSS to the public without registration,
SPSS agrees to use its reasonable efforts to (i) make and keep public
information available, as those terms are understood and defined in Commission
Rule 144, at all times: (ii) file with the Commission in a timely manner all
reports and other documents required of SPSS under the 1933 Act and the Exchange
Act; and (iii) furnish to Buyer forthwith upon request a written statement by
SPSS that it has complied with the reporting requirements of the Exchange Act, a
copy of the most recent annual or quarterly report of SPSS, and such other
reports and documents so filed by SPSS as may be reasonably requested in
availing Buyer of any rule or regulation of the Commission permitting the sale
of any securities of SPSS held by Buyer without registration. SPSS shall provide
Buyer with a written notice if it breaches any of its obligations under this
Section 5(a). In the event SPSS

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breaches any of its obligations under this Section 5(a) in a manner that renders
the benefits of Commission Rule 144 unavailable to Buyer during the continuance
of such breach Buyer determines that it wants to sell any Shares pursuant to
Commission Rule 144, Buyer shall provide SPSS with a written notice requesting
that such breach be cured (a "Cure Notice"). If any such breach is not cured in
a manner that restores the benefits of Commission Rule 144 within a period of at
least 60 days after the delivery of a Cure Notice by Buyer to SPSS, then, at the
option of Buyer, exercisable at any time during the continuance of such breach,
SPSS shall repurchase from Buyer, at a price per share equal to the Current
Market Price (as defined below), the lesser of (x) all Shares then beneficially
owned by the Buyer and (y) the number of Shares that multiplied by the Current
Market Price would equal $3.2 million of total purchase price by SPSS. Buyer may
exercise such option by delivering to SPSS a written notice of such exercise (a
"Purchase Notice"), and the parties shall consummate such repurchase on a date
specified by Buyer in such Purchase Notice, which date may be no earlier than
ten days after the date such Purchase Notice is delivered to SPSS. SPSS shall
pay such purchase price by wire transfer of immediately available funds to an
account designated by Buyer in such Purchase Notice, against delivery to SPSS of
the certificates representing the repurchased Shares. In the event SPSS
repurchases less than all of the Shares then owned by Buyer, it shall promptly
deliver to Buyer a new certificate representing such remaining Shares. As used
herein, "Current Market Price" means the average of the closing prices of SPSS
Common Stock, as quoted on the Nasdaq National Market, for the five trading days
immediately preceding the date such Purchase Notice is delivered by Buyer to
SPSS.

                           (b) SPSS COOPERATION. If at any time Buyer elects to
sell securities of SPSS without registration, SPSS shall cooperate with Buyer in
connection with such sale and promptly take all action as may be reasonably
requested by Buyer to effectuate such sale, including without limitation: (i)
providing such information and executing such instruments and documents as Buyer
may reasonably request, (ii) when securities of SPSS held by Buyer become
eligible for resale under Commission Rule 144(k), taking all actions necessary
to cause SPSS's transfer agent to promptly remove all restrictive legends from
the certificates representing such securities, and (iii) when any securities of
SPSS held by Buyer that are not eligible for resale under Commission Rule 144(k)
are sold in compliance with Commission Rule 144, taking all actions necessary to
cause SPSS's transfer agent to promptly remove all restrictive legends from the
certificates representing such securities."

         4. Deletion of Sections 6 and 7. Sections 6 and 7 are deleted in their
entirety.

         5. This Amendment shall be governed by and construed in accordance with
the laws of the State of Illinois, without giving effect to its conflict of laws
principles.

         6. This Amendment may be executed by facsimile and in any number of
counterparts, each of which shall be deemed an original and enforceable against
the parties actually executing such counterpart, and all of which together shall
constitute one instrument.

         7. The Agreement and this Amendment constitute the entire agreement
among the parties relative to the specific subject matter hereof. Except as
amended hereby, the Agreement remains in full force and effect in accordance
with its original terms. After giving effect to this Amendment, only the
following provisions of the Agreement shall continue in effect: Section 2,
Section 3, Section 4(b), Section 4(c), Section 4(d), Section 4(e) (i) and (iv),
Section 5 (as amended hereby) and Section 8.

                                      -2-
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         IN WITNESS WHEREOF, the undersigned have executed this Amendment to the
Stock Purchase Agreement, dated as of October 22, 2001, by and between SPSS and
Buyer as of the day and year first above written.

                                SPSS:

                                SPSS INC.

                                By:  /s/ Edward Hamburg
                                   --------------------------------------------
                                     Name:  Edward Hamburg
                                     Title: Executive Vice President Corporate
                                            Operations, Chief Financial Officer
                                            and Secretary

                                BUYER:

                                AMERICA ONLINE, INC.

                                By:  /s/ Frank Marvin
                                   --------------------------------------------
                                     Name:  Frank Marvin
                                     Title: Senior Vice President of Marketing

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