<PAGE>
                                                                  Exhibit 10.100


                               SECOND AMENDMENT TO
           ONE NINETY ONE PEACHTREE ASSOCIATES JOINT VENTURE AGREEMENT

            This Second Amendment (this "Amendment") to One Ninety One Peachtree
Associates Joint Venture Agreement (the "Venture Agreement") is entered into as
of October 27, 1997, by and among C-H ASSOCIATES, LTD., a Georgia limited
partnership ("CHV") and DIHC PEACHTREE ASSOCIATES, a Georgia general partnership
("DIHC"). All capitalized terms used herein shall have the meanings given to
them in the Venture Agreement.

            WHEREAS, One Ninety One Peachtree Associates (the "Venture") was
formed pursuant to the Joint Venture Agreement dated February 1, 1988 and was
amended pursuant to First Amendment, dated as of February 28, 1993 (as so
amended, the "Venture Agreement");

            WHEREAS, Cornerstone Properties Inc., a Nevada corporation
("Cornerstone"), directly or indirectly, has acquired all of the beneficial
ownership of DIHC and in connection therewith has entered into certain
agreements with CHV;

            WHEREAS, CHV and DIHC desire to amend the Venture Agreement as set
forth in this Amendment for certain purposes described herein;

            NOW THEREFORE, in consideration of the mutual covenants herein
contained, and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

            1. CHV consents to the acquisition by Cornerstone of all of the
      beneficial ownership of DIHC and agrees that the same shall not constitute
      a breach or violation of Section 6.01 or any other provisions of the
      Venture Agreement so long as DIHC and Cornerstone comply with the
      provisions of Section 6.01 and any other provision of the Venture
      Agreement in connection with the consummation of such acquisition. DIHC
      hereby represents and warrants to the Venture and CHV that the acquisition
      of all of the beneficial ownership of DIHC by Cornerstone was accomplished
      in compliance with all applicable state or federal securities laws. In
      connection therewith, DIHC hereby agrees to indemnify and hold harmless
      the Venture and CHV from and against any and all costs, damage, injury,
      claims, actions and demands (including, without limitation, attorney's
      fees) suffered by the Venture or CHV as a result of any violation or
      alleged violation or failure to comply or alleged failure to comply with
      any state or federal securities laws.

            2. Section 1.01 shall be amended by replacing the existing
      definitions as follows:


                                        1
<PAGE>

            DIHC Affiliate. The term "DIHC Affiliate" means (i) Cornerstone,
      (ii) any Person which is wholly owned by Cornerstone, and (iii) any other
      Person which, directly or indirectly, through one or more intermediaries,
      controls or is controlled by, or is under common control with any of the
      aforementioned DIHC Affiliates, or any of them. The term "control," as
      used in the immediately preceding sentence, means, with respect to a
      Person that is a corporation or partnership, the right to the exercise,
      directly or indirectly of more than 25% of the voting rights attributable
      to the shares of the controlled corporation or ownership of the right to
      receive 25% or more of the profits of the controlled partnership, and,
      with respect to a Person that is not a corporation or a partnership, the
      possession, directly or indirectly, of not less than 25% of the beneficial
      ownership thereof.

            3. Section 3.01(c)(xvii) is hereby amended by inserting "(A)" before
      the word "Approval" in the first line of Section 3.01(c)(xvii) and by
      adding the following new subsections (B) and (C) to the end thereof:

            "(B) Notwithstanding the foregoing, DIHC and CHV agree that at all
      times prior to the earlier to occur of (i) the Lock-Out Date or (ii) the
      date on which the combined Percentage Interests in the Venture of DIHC and
      any DIHC Affiliate is not greater than 50% notwithstanding that CHV is the
      Managing Partner of the Venture, DIHC shall have the authority to manage
      and direct the leasing of space in the Property on behalf of the Venture
      and to Approve all leasing matters with respect to the Property, to the
      extent consistent with the Annual Budget and the Marketing Plans, without
      the need of Approval from CHV. It is understood and agreed that the
      Leasing Agent shall from time to time submit to DIHC for Approval on
      behalf of the Venture recommendations with respect to new leases and other
      leasing matters in the form of Leasing Agent Recommendations. It is
      further understood and agreed that if DIHC shall desire to enter into any
      new lease or implement any other leasing matter that is not the subject of
      a Leasing Agent Recommendation, DIHC shall give written notice to Leasing
      Agent at least ten (10) days prior to entering into such lease or
      implementing such other leasing matter so as to provide Leasing Agent the
      opportunity to submit to DIHC a Leasing Agent Recommendation with respect
      to such proposed new lease or other leasing matter. DIHC shall have the
      right to Approve or disapprove such recommendations unilaterally and
      without the need for any further Approval from CHV and, once Approved,
      DIHC shall oversee the implementations of the Leasing Agent
      Recommendations relating to leasing matters and execute all leases and all
      other documents and instruments relating to leasing matters on behalf of
      the Venture. The Venture shall cause Leasing Agent, at the expense of the
      Venture, to furnish or where appropriate make available to DIHC, such
      documents and information as DIHC shall reasonably request in order to
      enable DIHC to evaluate such Leasing Agent Recommendations relating to
      leasing matters. The failure of DIHC to Approve or disapprove any Leasing
      Agent Recommendation within ten (10) days after receipt by DIHC of such
      Leasing Agent Recommendation together with all additional information


                                        2
<PAGE>

      reasonably requested by DIHC pertaining thereto shall be deemed the
      Approval of DIHC of such Leasing Agent Recommendation and Leasing Agent
      shall be entitled to implement same, provided, however, the Leasing Agent
      Recommendation shall state in capitalized letters that: "THE FAILURE TO
      RESPOND TO THIS LEASING AGENT RECOMMENDATION WITHIN 10 DAYS AFTER RECEIPT
      OF THIS NOTICE AND ANY REASONABLY REQUESTED ADDITIONAL INFORMATION
      PERTAINING HERETO SHALL BE DEEMED YOUR APPROVAL TO SUCH LEASING AGENT
      RECOMMENDATION." If DIHC is unwilling or unable to Approve or disapproves
      such Leasing Agent Recommendation, after consultation and discussion with
      the Leasing Agent, then the resolution of such matters may be submitted by
      DIHC or the Leasing Agent, to the "Venture Operations Arbitration Process"
      for resolution as hereinbelow described."

            "Venture Operations Arbitration Process" shall mean the process for
      resolution of any dispute between DIHC and the Leasing Agent in connection
      with a Leasing Agent Recommendation. Either of the Leasing Agent or DIHC
      may invoke this arbitration process by the giving of written notice to the
      other, which notice shall state that the invoking party believes an
      impasse exists as to a Leasing Agent Recommendation.

            If Leasing Agent or DIHC invokes the arbitration process, then,
      within five (5) days after the non-invoking party receives notice from the
      invoking party, Leasing Agent and DIHC shall each place in separate sealed
      envelopes its final good faith proposal as to the Leasing Agent
      Recommendation and shall open and exchange their final proposals in each
      other's presence (the "Final Proposals"). If Leasing Agent and DIHC cannot
      then agree on the Leasing Agent Recommendation within five (5) days
      thereafter, the matter shall be determined in accordance with the rules of
      the American Arbitration Association, except as modified by this
      provision. If Leasing Agent or DIHC fails to prepare its Final Proposal or
      to cooperate with the other party to open and exchange the Final Proposals
      of the parties, and if such failure shall continue for a period of five
      (5) days after the date the Final Proposals were to be opened and
      exchanged, then the Final Proposal of the non-failing party shall
      constitute the determination pursuant to this process.

            Unless Leasing Agent and DIHC can agree upon a single arbitrator
      prior to the time they are required to designate their party-arbitrators,
      there shall be three arbitrators (the "Panel"), each of whom shall have
      significant experience in dealing with matters similar to the matter in
      dispute with respect to sizeable commercial properties in the Atlanta
      metropolitan area and none of whom shall have any current or prior
      connection or affiliation with either of the Venturers.

            If required, the following procedure shall be used for the selection
      of the Panel. Leasing Agent and DIHC shall each specify by notice to the
      other on or prior to the


                                        3
<PAGE>

      fifth (5th) day after the Final Proposals were exchanged the name and
      address of the person designated to act as party-arbitrator on its behalf.
      The party-arbitrators so chosen shall meet within five (5) days after
      their appointment and select a third arbitrator. If Leasing Agent or DIHC
      fails to notify the other of the appointment of its party-arbitrator, as
      aforesaid, within or by the time above specified, then the Final Proposal
      of the party who timely selected a party-arbitrator shall constitute the
      determination pursuant to this process.

            If, within five (5) days after the party-arbitrators are appointed,
      the said two party-arbitrators are unable to agree upon the appointment of
      the third arbitrator, then either party, on behalf of both, may request
      the American Arbitration Association in Atlanta, Georgia to appoint the
      third arbitrator in accordance with its rules. In the event of the
      failure, refusal or inability of any arbitrator to act, a new arbitrator
      shall be appointed in his stead, which appointment shall be made in the
      same manner as hereinabove provided for the appointment of such arbitrator
      so failing, refusing or being unable to act.

            Within five (5) days after the selection of the single arbitrator
      or, if required, within one business day after the selection of the Panel,
      DIHC and Leasing Agent shall submit a written statement to the arbitrator
      or Panel specifying the reasons their Final Proposal as to the Leasing
      Agent Recommendation should be selected. The arbitrator or Panel shall
      make its decision within five (5) days after such submission. The
      arbitrator or Panel shall select either the Leasing Agent's or DIHC's
      Final Proposal, whichever in the arbitrator's or Panels's judgment
      represents the most appropriate recommendation for preserving and
      enhancing the long-term value of the Property. The Panel shall reach its
      decision by majority vote. The arbitrator or the Panel shall communicate
      its decision by written notice to the Leasing Agent and DIHC.

            Such determination shall be final, binding and conclusive upon both
      DIHC and the Leasing Agent and shall be non-appealable and enforceable in
      any court having jurisdiction. All hearings and proceedings before the
      arbitrator or the Panel shall be held in Atlanta, Georgia.

            If a single arbitrator is selected, each party shall share such
      arbitrator's fees and expenses equally. If a Panel is selected, each party
      shall pay the fees and expenses of its party-arbitrator, and the fees and
      expenses of the third arbitrator shall be borne equally by the parties.
      Notwithstanding the foregoing, the arbitrator or the Panel may conclude
      that one of the parties acted in bad faith, in which event such party
      shall pay 100% of the fees and expenses of the arbitrator or the Panel, as
      the case may be.

            (C) In the event DIHC elects to become the Managing Partner pursuant
      to Section 3.01(e), upon termination of DIHC as the Managing Partner for
      any reason,


                                        4
<PAGE>

      the provisions of subsection (B) of this Section 3.01(c)(xvii) shall no
      longer be deemed applicable;

            4. Section 3.01 is hereby further amended by adding the following
new subsections (e), (f) and (g) following subsection (d) thereof:

            "(e) DIHC may elect to be the Managing Partner instead of CHV at any
      time, without cause, prior to the Lock-Out Date but only for so long as
      the combined Percentage Interests in the Venture of DIHC and any DIHC
      Affiliates shall exceed 50%. This right is personal to DIHC and its DIHC
      Affiliates, and this right may not be assigned to or exercised by any
      Person that is not DIHC or a DIHC Affiliate. To exercise such election,
      DIHC must give at least ninety (90) days' prior written notice to CHV. In
      the event DIHC elects to become the Managing Partner pursuant to this
      Section 3.01(e), the following shall apply:

                  (1) In the event DIHC becomes the Managing Partner, it is
            understood that the Property Manager shall from time to time submit
            to DIHC for Approval on behalf of the Venture recommendations with
            respect to the Annual Budget and other matters involving management,
            operation, maintenance and improvement of the Property ("Property
            Manager Recommendations"). It is further understood and agreed that
            if DIHC shall desire to adopt an Annual Budget or take action on
            other matters involving management, operation, maintenance and
            improvement of the Property that is not the subject of a Property
            Manager Recommendation, DIHC shall give written notice thereof to
            Property Manager, together with a reasonably detailed written
            explanation thereof, at least ten (10) days prior to adopting such
            Annual Budget or taking such action, as the case may be, so as to
            provide Property Manager the opportunity to submit to DIHC a
            Property Manager Recommendation with respect to such proposed Annual
            Budget and/or other action. DIHC, as the Managing Partner, shall
            have the right to Approve or disapprove such recommendations
            unilaterally and without the need for any further Approval from CHV
            and once Approved, DIHC shall oversee the implementation of the
            Property Manager Recommendations. The Property Manager shall, at the
            expense of the Venture, furnish or where appropriate make available
            to DIHC, such documents and information as DIHC shall reasonably
            request in order to enable DIHC to evaluate such recommendation. The
            failure of DIHC to Approve or disapprove any Property Manager
            Recommendation within ten (10) days after receipt by DIHC of such
            Property Manager Recommendation together with all additional
            information reasonably requested by DIHC pertaining thereto shall be
            deemed the Approval of DIHC of such Property Manager Recommendation
            and Property Manager shall be entitled to implement same, provided,
            however, the Property Manager Recommendation shall state in
            capitalized letters that: "THE FAILURE TO


                                        5
<PAGE>

            RESPOND TO THIS PROPERTY MANAGER RECOMMENDATION WITHIN 10 DAYS AFTER
            RECEIPT OF THIS NOTICE AND ANY REASONABLY REQUESTED ADDITIONAL
            INFORMATION PERTAINING HERETO SHALL BE DEEMED YOUR APPROVAL TO SUCH
            PROPERTY MANAGER RECOMMENDATION." If DIHC is unwilling or unable to
            Approve or disapproves such Property Manager Recommendation, after
            consultation and discussion with the Property Manager, then the
            resolution of such matters may be submitted by DIHC or the Property
            Manager to the "Venture Operations Arbitration Process" for
            resolution as hereinbelow described.

                  "Venture Operations Arbitration Process" shall mean the
            process for resolution of any dispute between DIHC and the Property
            Manager in connection with a Property Manager Recommendation. Either
            of the Property Manager or DIHC may invoke this arbitration process
            by the giving of written notice to the other, which notice shall
            state that the invoking party believes an impasse exists as to a
            Property Manager Recommendation.

                  If Property Manager or DIHC invokes the arbitration process,
            then, within five (5) days after the non-invoking party receives
            notice from the invoking party, Property Manager and DIHC shall each
            place in separate sealed envelopes its final good faith proposal as
            to the Property Manager Recommendation and shall open and exchange
            their final proposals in each other's presence (the "Final
            Proposals"). If Property Manager and DIHC cannot then agree on the
            Property Manager Recommendation within five (5) days thereafter, the
            matter shall be determined in accordance with the rules of the
            American Arbitration Association, except as modified by this
            provision. If Property Manager or DIHC fails to prepare its Final
            Proposal or to cooperate with the other party to open and exchange
            the Final Proposals of the parties, and if such failure shall
            continue for a period of five (5) days after the date the Final
            Proposals were to be opened and exchanged, then the Final Proposal
            of the non-failing party shall constitute the determination pursuant
            to this process.

                  Unless Property Manager and DIHC can agree upon a single
            arbitrator prior to the time they are required to designate their
            party-arbitrators, there shall be three arbitrators (the "Panel"),
            each of whom shall have significant experience in dealing with
            matters similar to the matter in dispute with respect to sizeable
            commercial properties in the Atlanta metropolitan area and none of
            whom shall have any current or prior connection or affiliation with
            either of the Venturers.

                  If required, the following procedure shall be used for the
            selection of the Panel. Property Manager and DIHC shall each specify
            by notice to the other on


                                        6
<PAGE>

            or prior to the fifth (5th) day after the Final Proposals were
            exchanged the name and address of the person designated to act as
            party-arbitrator on its behalf. The party-arbitrators so chosen
            shall meet within five (5) days after their appointment and select a
            third arbitrator. If Property Manager or DIHC fails to notify the
            other of the appointment of its party-arbitrator, as aforesaid,
            within or by the time above specified, then the Final Proposal of
            the party who timely selected a party-arbitrator shall constitute
            the determination pursuant to this process.

                  If, within five (5) days after the party-arbitrators are
            appointed, the said two party-arbitrators are unable to agree upon
            the appointment of the third arbitrator, then either party, on
            behalf of both, may request the American Arbitration Association in
            Atlanta, Georgia to appoint the third arbitrator in accordance with
            its rules. In the event of the failure, refusal or inability of any
            arbitrator to act, a new arbitrator shall be appointed in his stead,
            which appointment shall be made in the same manner as hereinabove
            provided for the appointment of such arbitrator so failing, refusing
            or being unable to act.

                  Within five (5) days after the selection of the single
            arbitrator or, if required, within one business day after the
            selection of the Panel, DIHC and Property Manager shall submit a
            written statement to the arbitrator or Panel specifying the reasons
            their Final Proposal as to the Property Manager Recommendation
            should be selected. The arbitrator or Panel shall make its decision
            within five (5) days after such submission. The arbitrator or Panel
            shall select either the Property Manager's or DIHC's Final Proposal,
            whichever in the arbitrator's or Panels's judgment represents the
            most appropriate recommendation for preserving and enhancing the
            long-term value of the Property. The Panel shall reach its decision
            by majority vote. The arbitrator or the Panel shall communicate its
            decision by written notice to the Property Manager and DIHC.

                  Such determination shall be final, binding and conclusive upon
            both DIHC and the Property Manager and shall be non-appealable and
            enforceable in any court having jurisdiction. All hearings and
            proceedings before the arbitrator or the Panel shall be held in
            Atlanta, Georgia.

                  If a single arbitrator is selected, each party shall share
            such arbitrator's fees and expenses equally. If a Panel is selected,
            each party shall pay the fees and expenses of its party-arbitrator,
            and the fees and expenses of the third arbitrator shall be borne
            equally by the parties. Notwithstanding the foregoing, the
            arbitrator or the Panel may conclude that one of the parties acted
            in bad faith, in which event such party shall pay 100% of the fees
            and expenses of the arbitrator or the Panel, as the case may be.


                                        7
<PAGE>

                  (2) If DIHC (or a DIHC Affiliate) becomes the Managing Partner
            pursuant to this Section 3.01(e) and thereafter the combined
            Percentage Interests in the Venture of DIHC and any DIHC Affiliates
            shall not be greater than 50%, then provided that either a Hines
            Affiliate or a Cousins Affiliate is then a managing general partner
            of CHV, CHV shall automatically become the Managing Partner of the
            Venture instead of such non-affiliated Person, without cause
            effective as of the date which is sixty (60) days after such
            transfer to the non-affiliated Person.

                  (3) Upon the occurrence of the Lock-Out Date, provided that a
            Hines Affiliate or a Cousins Affiliate is then a managing general
            partner of CHV, CHV shall automatically become the Managing Partner
            of the Venture instead of DIHC, without cause, effective on the day
            following the occurrence of the Lock-Out Date.

            (f) Upon termination of DIHC as the Managing Partner for any reason,
      the provisions of paragraph (e) above shall no longer be deemed
      applicable.

            (g) Upon termination of any Venturer as the Managing Partner for any
      reason, the terminated Managing Partner shall deliver to the new Managing
      Partner the following with respect to the Property and other assets and
      liabilities of the Venture:

                  (1) A final accounting, reflecting the balance of income and
            expenses as of the date of termination to be delivered within thirty
            (30) days after such termination.

                  (2) Control of any balance or monies of the Venture or tenant
            security deposits, or both, including, without limitation, all funds
            in any bank accounts held by the Managing Partner with respect to
            the Venture or its properties, to be delivered immediately upon such
            termination.

                  (3) All records, contracts, leases, receipts for deposits,
            unpaid bills and other papers or documents which are in the Managing
            Partner's possession or are reasonably obtainable by the Managing
            Partner and which pertain to the Venture or its properties to be
            delivered immediately upon such termination."

            5. Section 3.04(a) is hereby amended by deleting the names "Herman
A. Vonhof or Charles W. Strawser, Jr." and substituting in lieu thereof the
names "John S. Moody or Rodney C. Dimock" and by deleting the names "Vipin L.
Patel or Charles L. Davidson, III" and substituting in lieu thereof "Daniel M.
DuPree" or "C. Kevin Shannahan".

            6. Section 4.02(e)(vii) is hereby amended to read as follows:


                                        8
<PAGE>

            "(vii) For purposes of this provision, the term "liquidation" shall
      have the meaning set forth in the first sentence of Treasury Regulation
      Section 1.704-1(b)(2)(ii)(g), but shall not include a constructive
      liquidation of the Venture caused by a termination under Section 708(b)(1)
      of the Code."

            7. Section 5.08 is hereby amended by deleting the first sentence in
subsection (b) and substituting the following in lieu thereof:

      "In addition to all other remedies set forth herein, if the Defaulting
      Venturer is the Managing Partner, the Non-Defaulting Venturer shall have
      the right to remove the Defaulting Venturer as Managing Partner and
      designate a new Managing Partner."

            8. Section 6.01 is hereby amended by adding the following to the end
of subsection (d) thereof:

      "To the extent any Venturer is now or hereafter beneficially owned or
      controlled, directly or indirectly, by any Person which is
      publicly-traded, the sale or transfer or other disposition of all or part
      of the stock in such publicly-traded Person shall not be considered a
      "Transfer" within the meaning of this Agreement."

            9. Section 6.02(j) is hereby deleted in its entirety.

            10. Section 6.02 shall be amended by adding a new subsection 6.02(j)
following subsection (i) as follows:

            (j) In addition to all other permitted Transfers, and subject to
      Section 6.02(f) above, DIHC may Transfer its entire Percentage Interest in
      the Venture to an operating limited partnership in which the sole general
      partner is DIHC or a DIHC Affiliate (the "Operating Partnership") or to
      any Person which is, directly or indirectly, wholly-owned by the Operating
      Partnership, provided that the limited partners of the Operating
      Partnership have the right to convert their respective limited partner
      units in the Operating Partnership ("Units") into stock of Cornerstone or
      an Affiliated Entity of Cornerstone which is a publicly-traded entity on a
      one-for-one basis (that is, a single Unit shall be exchangeable for a
      single share of common stock of Cornerstone or an Affiliated Entity of
      Cornerstone which is a publicly-traded entity on a national securities
      exchange or through the NASDAQ national marketing system.)

            11. Section 5.02 shall be amended by adding new subsection 5.02(k)
as follows:

            (k) If, following the admission of the Operating Partnership or an
      Affiliated Entity thereof to the Venture as the successor to DIHC, an
      Offer is made pursuant to Section 5.02 and the Operating Partnership or an
      Affiliated Entity thereof is the


                                        9
<PAGE>

      purchasing Venturer, CHV, at its option, may elect to cause the purchasing
      Venturer to acquire all or part of CHV's interest in the Venture in
      exchange for Units, and, in the event of such election the minimum
      purchase price for CHV's interest in the Venture shall be $1,000.00. In
      the event CHV elects to receive Units in consideration for the transfer of
      all or any part of its interest in the Venture, CHV shall by written
      notice to the Operating Partnership delivered no later than ten (10) days
      prior to the Closing of the buy/sell, designate the portion of the
      purchase price which it desires to receive in cash and the portion of the
      purchase price (expressed in dollars) it desires to receive in Units.
      Provided the Operating Partnership receives such notice in a timely
      manner, at the Closing the cash portion of the purchase price paid by the
      Operating Partnership shall be in the amount designated by CHV to be paid
      in cash and the balance of the purchase price shall be paid in Units to
      CHV (or its designee or designees) the dollar value of which, if such
      Units are convertible into common shares of Cornerstone, shall be
      determined based on the average of the closing price for shares of stock
      of Cornerstone on The New York Stock Exchange for the five (5) consecutive
      trading days ending on the trading day immediately preceding the date of
      Closing, and if such Units are convertible into common shares of any
      Affiliated Entity of Cornerstone which is a publicly-traded entity on a
      national securities exchange or on the NASDAQ national marketing system,
      shall be determined based on the average of the closing price for shares
      of stock of such publicly-traded entity for the five (5) consecutive
      trading days ending on the trading day immediately preceding the date of
      Closing (as described above, it being acknowledged and agreed that any
      holder of Units shall have the right to elect to exchange all or any
      portion of such Units for shares of common stock of Cornerstone or an
      Affiliated Entity thereof which is a publicly- traded entity on a
      one-for-one basis.) In the event that (i) CHV elects to contribute all or
      part of its interest in the Venture in exchange for Units, and (ii) the
      amount of Operating Partnership liabilities that would be allocable to CHV
      under section 752 of the Code immediately following the contribution would
      be less than CHV's pre-contribution share of Venture liabilities
      (including as a result of the extinguishment or contribution to capital of
      any Venture liabilities held by Cornerstone or its affiliates) and thereby
      cause CHV and its partners to recognize gain for federal income tax
      purposes, DIHC shall, and shall cause Cornerstone, the Operating
      Partnership and any other DIHC Affiliate to, cooperate with CHV in good
      faith in implementing one or more alternative measures to have the
      Operating Partnership's liabilities allocable to CHV under section 752 of
      the Code equal or exceed CHV's precontribution share of Venture
      liabilities so that CHV does not recognize taxable gain as a result of the
      contribution, including guaranties by CHV of the "bottom-side" portion of
      one or more Operating Partnership nonrecourse liabilities and/or the
      assumption by CHV of partial or full deficit capital account liability,
      provided that neither DIHC, Cornerstone nor the Operating Partnership
      shall be required to approve any such measures to the extent that they
      would adversely affect the tax position of any other limited partner of
      the Operating Partnership. The foregoing shall not in any way preclude
      DIHC, Cornerstone or the Operating Partnership from taking any action that
      would result in the extinguishment of


                                       10
<PAGE>

      Venture liabilities held by Cornerstone or its Affiliates in connection
      with such contribution.

            12. Section 8.01 is hereby amended by deleting the names and
addresses in subsection (b) thereof and substituting the following in lieu
thereof:

                  Hines Interests Limited Partnership
                  70 West Madison
                  Suite 440
                  Chicago, Illinois 60602
                  Attn: C. Kevin Shannahan

                  With a copy to:

                  Cousins Real Estate Corporation
                  2500 Windy Ridge Parkway
                  Suite 1600
                  Atlanta, Georgia 30339
                  Attn: Corporate Secretary

                  and to:

                  Hines Interests Limited Partnership
                  2800 Post Oak Boulevard
                  Houston, Texas 77056
                  Attn: Jeffrey C. Hines

            13. Section 8.01 is hereby amended by deleting the names and
addresses in subsection (c) thereof and substituting the following in lieu
thereof:

                  Cornerstone Properties Inc.
                  126 East 56th Street
                  New York, New York 10022
                  Attention:  John S. Moody
                              Rodney C. Dimock

                  King & Spalding
                  191 Peachtree Street
                  Atlanta, Georgia 30303-1763
                  Attention: William B. Fryer, Esq.

            14. Section 8.12(b) is hereby deleted in its entirety.


                                       11
<PAGE>

            15. For so long as the Permanent Loan remains outstanding, DIHC
agrees that no person or entity that is a partner of the Venture or who would be
treated as a partner of such partnership for federal income tax purposes shall
be the owner of such debt for federal income tax purposes, unless CHV otherwise
consents in writing.

            16. The parties hereto acknowledge and agree that the Lock-Out Date
is February 28, 2002.

            17. Capitalized terms used but not defined herein shall have the
same respective meanings given such terms in the Venture Agreement.

            18. The Venture Agreement, as amended by this Amendment, is hereby
ratified and confirmed and remains in full force and effect.


                                       12
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have executed the Amendment
under seal as of the date first written above.

                         CHV:

                         C-H ASSOCIATES, LTD., a Georgia limited partnership,
                         by its only two general partners

                         By:   Cousins Real Estate Corporation, a Georgia
                               corporation

                               By: /s/
                                   ------------------------
                               Name:  Peter A. Tortohoff
                                      ---------------------
                               Title: Senior V.P
                                      ---------------------

                               Attest: /s/
                                       --------------------
                               Name:   Tom G. Charlesworth
                                       --------------------
                               Title:  Sec.
                                       --------------------

                                      [CORPORATE SEAL]


                                       13
<PAGE>

                         By:   Hines Peachtree Associates I Limited Partnership,
                               a Texas limited partnership, by its only two
                               general partners

                               By: /s/                 (Seal)
                                   --------------------
                                   Gerald D. Hines

                               By:   Hines Atlanta Corporation, a Georgia
                                     corporation

                                     By: /s/
                                         ------------------------
                                     Name:   Gerald D. Hines
                                             ---------------------
                                     Title:  President
                                             ---------------------

                                     Attest: /s/
                                             --------------------
                                     Name:   Jeanne E. Hutchens
                                     Title:  Assistant Secretary

                                           [CORPORATE SEAL]


                                       14
<PAGE>

                               DIHC

                               DIHC PEACHTREE ASSOCIATES, a Georgia general
                               partnership, by its only two general partners

                               By:   DIHC Atlanta, Inc., a Georgia corporation

                                     By: /s/
                                         -------------------------
                                     Name:   Kevin Mahoney
                                             ---------------------
                                     Title:
                                             ---------------------

                                     Attest: /s/
                                             ---------------------
                                     Name:   Thomas Laftus
                                             ---------------------
                                     Title:  Secretary
                                             ---------------------

                                                 [CORPORATE SEAL]


                               By:   DIHC Peachtree, Inc., a Georgia corporation

                                     By: /s/
                                         -------------------------
                                     Name:   Kevin Mahoney
                                             ---------------------
                                     Title:
                                             ---------------------

                                     Attest: /s/
                                             ---------------------
                                     Name:   Thomas Laftus
                                             ---------------------
                                     Title:  Secretary
                                             ---------------------

                                                 [CORPORATE SEAL]


                                       15
<PAGE>

                         Consented and Agreed to:

                         LEASING AGENT

                         C-H LEASING ASSOCIATES, a Georgia general
                         partnership, by its two general partners

                               By:   Cousins Real Estate Corporation, a Georgia
                                     corporation

                                     By: /s/
                                         --------------------------
                                     Name: Peter A. Toutchaff
                                           ------------------------
                                     Title: S.V.P.
                                            -----------------------

                              By:   Hines Atlanta Realty, Inc., a Georgia
                                    corporation

                                    By: /s/
                                         --------------------------
                                    Name: C. Kevin Shannahan
                                          -------------------------
                                    Title: Executive Vice President
                                           ------------------------

                         PROPERTY MANAGER

                         C-H MANAGEMENT ASSOCIATES, a Georgia general
                         partnership, by its two general partners

                              By:   Cousins Real Estate Corporation, a Georgia
                                    corporation

                                    By: ______________________________
                                    Name: ____________________________
                                    Title: _____________________________

                              By:   /s/  Gerald D. Hines
                                    -----------------------------------
                                    Gerald D. Hines, President of Hines
                                    Properties, Inc., a general partner of C-H
                                    Management Associates.


                                       16