FIRST AMENDMENT TO STOCK PURCHASE AGREEMENT

     THIS FIRST AMENDMENT TO STOCK PURCHASE AGREEMENT (this "Amendment") is
entered into by and among CarrAmerica Realty Corporation ("CarrAmerica"),
OmniOffices (UK) Limited ("Omni UK"), OmniOffices (Lux) 1929 Holding Company
S.A. ("LuxCo"), VANTAS Incorporated ("VANTAS") and FrontLine Capital Group
(formerly known as Reckson Services Industries, Inc.) ("RSI") as of April
____, 2000.

                                   RECITALS:

     WHEREAS, CarrAmerica, Omni UK, LuxCo, VANTAS and RSI entered into a Stock
Purchase Agreement dated as of January 20, 2000 (such agreement, as
heretofore, hereby and hereinafter amended, the "UK Agreement") pursuant to
which CarrAmerica agreed to sell shares of common stock of Omni UK and LuxCo
owned by it together with its interest in certain loans made by it to Omni UK
and LuxCo to VANTAS on the terms set forth therein;

     WHEREAS, VANTAS, RSI, CarrAmerica, Omni UK and LuxCo have executed an
Agreement dated as of March 13, 2000, as amended, pursuant to which such
parties agreed to authorize certain actions governed by the UK Agreement;

     WHEREAS, the parties hereto wish to make certain additional amendments to
the UK Agreement; and

     WHEREAS, capitalized terms not otherwise defined herein shall have the
meanings set forth in the UK Agreement.

     NOW, THEREFORE, in consideration of the foregoing and the respective
covenants and agreements set forth herein, the parties, intending to be
legally bound, agree as follows:

     1. The second and third recitals of the UK Agreement are hereby deleted
in their entirety and replaced with the following:

        "WHEREAS, CarrAmerica has made certain loans to Omni UK and
        LuxCo as described on Exhibit B attached hereto, and may
        make additional loans to Omni UK and LuxCo as contemplated
        by Section 4.1(b)(iii) hereof (collectively, the "Loans"),
        which Loans are or will be evidenced by promissory notes,
        the date and denominations of which as of the date hereof
        are set forth on Exhibit B (the "Notes");

        WHEREAS, CarrAmerica desires to sell and transfer to VANTAS
        and VANTAS desires to purchase from CarrAmerica (i) the
        Notes in exchange for an amount equal to the principal
        amount of, and any accrued and unpaid interest with respect
        to, the Notes outstanding as of the Closing Date in
        accordance with Section 1.2 (the "Loan Consideration"), and
        (ii) all of the shares of non-voting common stock, par value
        (pound).01 per share, of Omni UK (which represents
        approximately 95% of the equity interest in Omni UK) (the
        "UK Non-Voting Common Stock") and all of the shares of
        non-voting common stock, par value $250 per share, of LuxCo
        (which represents approximately 95% of the equity interest
        in LuxCo) (the "Lux Non-Voting Common Stock"; and together
        with the UK Non-Voting Common Stock, collectively, the
        "Shares") owned of record by the Seller for total
        consideration equal to the "Share Consideration" as
        calculated pursuant to Annex A (the "Share Consideration");"

     2. Section 2.3 of the UK Agreement is hereby amended by inserting the
following at the end of Section 2.3:

        "Notwithstanding anything to the contrary contained herein,
        the parties acknowledge that, in connection with the
        consummation of the transactions contemplated by the Merger
        Agreement, the consent of the general partner of Mercury
        Executive Offices, L.P. may be required under the Limited
        Partnership Agreement dated November 16, 1998 and the
        management agreements related thereto; it being understood
        that Omni UK, LuxCo, VANTAS and RSI shall use commercially
        reasonable efforts to obtain such consent."

     3. Section 2.12(a) of the UK Agreement is hereby amended by deleting the
first sentence in its entirety and replacing it with the following:

        "Neither of the Companies nor any of their respective
        Subsidiaries owns any real property or interests in real
        property, other than OmniUK Real Property Leases (as defined
        below), LuxCo Real Property Leases (as defined below), the
        OmniUK Owned Property (as defined below) and certain
        interests in certain real property assets held directly or
        indirectly through the MAM Investment (as defined below)."

     4. The provision immediately following Section 2.13(j) on page 12 of the
UK Agreement is hereby deleted in its entirety and replaced with the
following:

        "; provided, however, that notwithstanding anything to the
        contrary contained herein other than any contracts relating
        to office equipment, maintenance or service for any
        individual business center of the Companies or their
        respective Subsidiaries which does not require annual
        payments in excess of $25,000, the sum of the aggregate
        future liabilities and costs of termination associated with
        all contracts, arrangements, agreements or understandings to
        which either of the Companies or any of their respective
        Subsidiaries is a party or by which they or any of their
        respective properties or assets which are not set forth on
        Schedule 5.2, 2.13 or 2.16 is bound does not exceed
        $5,000,000."

     5. Section 2.28 of the UK Agreement is hereby deleted in its entirety and
replaced with the following:

        "Section 2.28 MAM Investment. OmniUK and certain of its
        Subsidiaries have agreed to invest up to (pound)20 million
        in Mercury Executive Offices, L.P. on the terms and
        conditions set forth in the limited partnership agreement,
        dated November 16, 1998 (the "MAM Investment"), of which at
        least (pound)15,594,241 has been funded. Notwithstanding
        anything to the contrary contained herein, the parties
        acknowledge that, in connection with the consummation of the
        transactions contemplated by the Merger Agreement, the
        consent of the general partner of Mercury Executive Offices,
        L.P. may be required under the Limited Partnership Agreement
        dated November 16, 1998 and the management agreements
        related thereto; it being understood that Omni UK, LuxCo,
        VANTAS and RSI shall use commercially reasonable efforts to
        obtain such consent."

     6. Section 4.1(b)(iii) of the UK Agreement is hereby deleted in its
entirety and replaced with the following:

        "incur or assume any liabilities or incur any indebtedness
        for borrowed money, assume, guarantee, endorse or otherwise
        as an accommodation become responsible for the obligations
        of any other individual, corporation or entity (other than a
        wholly owned Subsidiary) except pursuant to contracts or
        agreements listed in Schedule 2.13 or except for loans and
        equity investments (which shall be deemed to be included on
        Exhibit A or Exhibit B, as applicable, attached hereto) by
        CarrAmerica necessary to fund the business of the Companies
        in the ordinary course or to fund committed developments;"

     7. Section 4.1(b)(v) of the UK Agreement is hereby deleted in its
entirety and replaced with the following:

        "make any material change in any Omni UK Real Property Lease
        or LuxCo Real Property Lease, as applicable, or other
        contracts or enter into, renew, fail to renew, terminate or
        permit to be terminated any Omni UK Real Property Lease or
        LuxCo Real Property Lease, as applicable, any other contract
        or agreement that calls for aggregate annual payments of
        $25,000 or more and which either (i) is not terminable by
        either of the Companies or their respective Subsidiary, as
        applicable, at will on 60 days or less notice without
        payment of a penalty or (ii) has a term of more than six
        months, other than the operating leases and related letters
        of comfort executed by Omni UK, LuxCo or any Subsidiaries
        thereof with respect to development and refurbishment
        projects identified in the CapEx Budget, as contemplated by
        the operating budgets for those projects;"

     8. Section 5.5 of the UK Agreement is hereby amended by inserting the
following sentence at the end of such section:

        "Not later than six months after the Closing, the Second
        Step Surviving Corporation shall reimburse CarrAmerica, as
        agent for itself and the stockholders of HQ Global
        Workplaces, Inc. ("HQ Global") immediately prior to the
        Closing (based on their proportionate indirect beneficial
        interests in Omni UK and LuxCo), for any additional lease
        deposits of Omni UK and LuxCo that are not identified on the
        disclosure schedules delivered in connection with the
        execution of this Agreement; provided that the Second Step
        Surviving Corporation is provided with a schedule of such
        additional lease deposits at or prior to Closing."

     9. Article 5 of the UK Agreement is hereby amended by adding the
following sections at the end of such Article 5:

        "Section 5.6 MAM Hammersmith Center. RSI and VANTAS hereby
        consent to the development of the MAM Hammersmith center.
        Immediately subsequent to the Closing, the Second Step
        Surviving Corporation shall reimburse CarrAmerica, as agent
        for itself and the stockholders of HQ Global immediately
        prior to the Closing (based on their proportionate indirect
        beneficial interests in Omni UK and LuxCo), for any costs
        that have been or will be incurred prior to Closing in
        connection with the development of the MAM Hammersmith
        center; provided that the Second Step Surviving Corporation
        is provided with a schedule of such amounts at or prior to
        Closing.

        Section 5.7 Prepaid Rent; Tenant Reimbursement. Immediately
        subsequent to the Closing, the Second Step Surviving
        Corporation shall pay to CarrAmerica, as agent for itself
        and the stockholders of HQ Global immediately prior to the
        Closing (based on their proportionate indirect beneficial
        interests in Omni UK and LuxCo), $576,000, which represents
        the amount of rent of Omni UK and LuxCo that was prepaid for
        the period after Closing;; provided that the Second Step
        Surviving Corporation is provided with a schedule of such
        amounts at or prior to Closing.

        Section 5.8 Capital Expenditures and Cash Fundings.
        Immediately subsequent to the Closing, the Second Step
        Surviving Corporation shall reimburse CarrAmerica, as agent
        for itself and the stockholders of HQ Global immediately
        prior to the Closing (based on their proportionate indirect
        beneficial interests in Omni UK and LuxCo), for all capital
        expenditures and development expenses of Omni UK or LuxCo
        incurred after April 30, 2000 and prior to Closing,
        including amounts funded to enable Omni UK to satisfy its
        capital commitments with respect to the MAM Investment;
        provided that the Second Step Surviving Corporation is
        provided with a schedule of such amounts at or prior to
        Closing.

        Section 5.9 Side Letter. At Closing, VANTAS shall assume the
        obligations of CarrAmerica with respect to that certain Side
        Letter dated as of November 16, 1998 by and among HQMerc UK
        Management Limited ("HQ Merc"), P.R.A. Investments Limited
        ("PRA"), P.K. Investments Limited ("PKL"), Peter Allport
        ("Allport"), Peter Kershaw ("Kershaw"), HQ Holdings Limited
        ("HQ Holdings") and CarrAmerica and that certain Side Letter
        dated as of November 16, 1998 by and among HQ Merc UK
        Partnership Limited, PRA, PKL, Allport, Kershaw, HQ Holdings
        and CarrAmerica."

     10. Section 6.2(b) of the UK Agreement is hereby deleted in its entirety
and replaced with the following:

        "CarrAmerica shall have received the cash required by Sections 1.2,
        5.3, 5.5, 5.6, 5.7 and 5.8."

     11. All references to "April 30, 2000" in Article X(a)(iv), Article
X(a)(vi) and Article X(a)(vii) of the UK Agreement are hereby changed to "May
31, 2000."

     12. All references to "May 1, 2000" in Article X(a)(iv) of the UK
Agreement are hereby changed to "June 1, 2000."

     13. The amount of the Loan Notes identified in Annex A to the UK
Agreement is hereby deleted and replaced with "21,229,392 (reduced by the
amount of any payments thereto prior to Closing)."

     14. Simultaneously with the execution of this Amendment, RSI shall
contribute $900,000 to VANTAS and VANTAS shall pay $900,000 in cash (the "UK
Stockholder Extension Payment") to CarrAmerica, as compensation for the
extension of the Closing Date from April 30, 2000 to May 31, 2000. The UK
Stockholder Extension Payment is nonrefundable and will not be used to adjust
the consideration otherwise payable in connection with the consummation of the
transactions contemplated by the UK Agreement.

     15. CarrAmerica, Omni UK and LuxCo represent and warrant, each as to
itself only, that each of CarrAmerica, Omni, UK and LuxCo has the requisite
capacity and authority, and has taken all actions necessary in order, to
execute, deliver and perform its obligations under this Amendment. This
Amendment is a legal, valid and binding obligation of each of CarrAmerica,
Omni UK and LuxCo, enforceable in accordance with its terms, except insofar as
enforcement thereof may be limited by bankruptcy, insolvency or other laws
relating to or affecting enforcement of creditors' rights generally including
such general equitable principles as may apply in the enforcement of
creditors' rights.

     16. VANTAS and RSI represent and warrant that each of VANTAS and RSI has
the requisite capacity and authority, and has taken all actions necessary in
order, to execute, deliver and perform its obligations under this Amendment.
This Amendment is a legal, valid and binding obligation of each of VANTAS and
RSI, enforceable in accordance with its terms, except insofar as enforcement
thereof may be limited by bankruptcy, insolvency or other laws relating to or
affecting enforcement of creditors' rights generally including such general
equitable principles as may apply in the enforcement of creditors' rights.

     17. This Amendment, the Merger Agreement, as amended, the Stock Purchase
Agreement, as amended, and the other agreements referred to herein and therein
represent the entire understanding of the parties with respect to the subject
matter contained herein. This Amendment may not be amended, modified or waived
except in a writing signed by the party against whom enforcement of such
amendment, modification or waiver is sought. This Amendment shall be construed
and interpreted in accordance with the laws of the State of Delaware, without
reference to the conflict of laws principles contained therein. This Amendment
may be executed in one or more counterparts, each of which shall be deemed an
original, but all of which, when taken together, shall constitute one and the
same instrument.

                           [signature page follows]

                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be duly executed as of the date first written above.


                                      CARRAMERICA REALTY CORPORATION



                                      By:  /s/ Karen B. Dorigan
                                          --------------------------
                                          Name:  Karen B. Dorigan
                                          Title: Managing Director



                                      OMNIOFFICES (UK) LIMITED


                                      By:  /s/ Thomas A. Carr
                                           ------------------------------
                                           Name: Thomas A. Carr
                                           Title: Director

                                      OMNIOFFICES (LUX) 1929 HOLDING
                                      COMPANY S.A.



                                      By:  /s/ Thomas A. Carr
                                           ------------------------------
                                           Name: Thomas A. Carr
                                           Title: Director


                                      FRONTLINE CAPITAL GROUP



                                      By: /s/ Jason Barnett
                                          --------------------------------
                                          Name: Jason Barnett
                                          Title:  Executive Vice President



                                      VANTAS INCORPORATED



                                      By:  /s/ Stephen M. Rathkopf
                                           -------------------------
                                           Name:  Stephen M. Rathkopf
                                           Title: Secretary