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                                                                   Exhibit 10.26


               FOURTH AMENDMENT OF OFFICE BUILDING LEASE AGREEMENT

         WHEREAS, TURNER ADREAC L.C., and NEON SYSTEMS, INC. ("Tenant") entered
into a certain Lease Agreement dated October 23, 1997 ("the Lease Agreement");
and

         WHEREAS, TA/Sugar Creek Place, Ltd., a Texas limited partnership
("Landlord"), acquired the Leased Premises and was assigned the Landlord's
interest under the Lease Agreement effective as of November 10, 1998;

         NOW, THEREFORE, the parties Landlord and Tenant hereby agree that the
Lease Agreement shall be amended as follows:

1.       The Leased Premises as defined in Section 1.01 of the Lease Agreement
         is hereby amended to mean and read;

         (a)      All of floor 5 of the Building calculated by Landlord to be
                  twenty five thousand nine hundred eighteen (25,918) square
                  feet of Net Rentable Area, and (b) all of floor 4 of the
                  building calculated by landlord to be twenty five thousand
                  eight hundred fourteen (25,814) square feet of Net Rentable
                  Area (same being Option Space 1, Option Space 2 and Option
                  Space 3 as referenced on Amended Exhibit H-1 of the Lease
                  Agreement) as reflected on the floor plan(s) of the Leased
                  Premises referenced Amended Exhibit B-1. Tenant shall have the
                  right to verify the Net Rentable Area of the Leased Premises
                  as so calculated by Landlord, and Landlord agrees to cooperate
                  with Tenant and tenants' architect with respect thereto.

2.       The leasehold improvements in Option Space 3 will be designed and
         constructed in accordance with Amended Exhibit H-1. Landlord
         acknowledges that Tenant is entitled to the full allowance of $16.50
         per square foot of Net Rentable Area in Option Space 3.

3.       Landlord acknowledges that in connection with Tenant's exercise of the
         Third Expansion Option, Tenant also elected to extend the Termination
         date of the Lease as to the initial Leased Premises, Option Space 1,
         Option Space 2 and Option Space 3 until the fifth anniversary of the
         Expansion Commencement Date of Option Space 3; accordingly, the
         termination Date of the Lease is now March 31, 2005 (subject to any
         adjustment of the Option Space 3 Expansion Commencement Date in
         accordance with Amended Exhibit H).

Except as changed and modified herein the terms and provisions of Lease
Agreement continue in full force and effect.

All capitalized terms used herein (and not otherwise defined herein) shall have
the meanings attributed to them in the Lease Agreement.

         IN WITNESS WHEREOF this instrument has been executed this __________
day of ______________________, 1999.

"LANDLORD"                              "TENANT"
TA/SUGAR CREEK PLACE LTD.               NEON SYSTEMS, INC.
A Texas limited partnership
By its general partner
Turner Adreac Management, L.C.
A Texas limited liability company

By:  _____________________________      By:  __________________________________
Name:    Michael Van                             Name:  John S. Reiland
Title:   Exec. Vice President                    Title     CFO