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                                                                   Exhibit 10.15

                    EIGHTH AMENDMENT TO AMENDED AND RESTATED
                        AGREEMENT OF LIMITED PARTNERSHIP
                                       OF
                     BRANDYWINE OPERATING PARTNERSHIP, L.P.

         THIS EIGHTH AMENDMENT, dated as of April 19, 1999 (the "Amendment"),
amends the Amended and Restated Agreement of Limited Partnership Agreement (as
heretofore amended to date, the "Partnership Agreement") of BRANDYWINE OPERATING
PARTNERSHIP, L.P., a Delaware limited partnership (the "Partnership").
Capitalized terms used herein but not defined herein shall have the meanings
given to such terms in the Partnership Agreement.

                                   BACKGROUND
                                   ----------

         A. Pursuant to the Partnership Agreement, Brandywine Realty Trust (the
"General Partner"), as the general partner of the Partnership, has the power and
authority to issue additional Partnership Interests and Units in one or more
newly created classes of Partnership Interests to persons on such terms and
conditions as the General Partner may deem appropriate.

         B. The General Partner, pursuant to the exercise of such power and
authority and in accordance with the Partnership Agreement, has determined to
execute this Amendment to the Partnership Agreement to create a new class of
Partnership Interests designated as the Series C Preferred Mirror Units having
designations, preferences and other rights which are substantially the same as
the economic rights of the 8.75% Series B Senior Cumulative Convertible
Preferred Shares of the General Partner (the "Series B Preferred Shares") and to
evidence the issuance of such additional Partnership Interests to the General
Partner in exchange for the General Partner's contribution to the Partnership of
the net proceeds of the sale of the Series B Preferred Shares.

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and other good and valuable consideration, the receipt,
adequacy and sufficiency of which are hereby acknowledged, the parties hereto,
intending to be legally bound, hereby amend the Partnership Agreement as
follows:

         8. In accordance with the Partnership Agreement, the Partnership
Agreement is hereby amended to establish, and to issue to the General Partner,
the Series C Preferred Mirror Units having the designations, preferences and
other rights set forth below:

                  (i)      Designation and Number. A class of Partnership
                           Interests designated as Series C Preferred Mirror
                           Units is hereby established. The number of Series C
                           Preferred Mirror Units shall be 4,375,000. The stated
                           value of each Series C Preferred Mirror Unit shall be
                           $24.00 (the "Stated Value").
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                  (ii)     Rank. The Series C Preferred Mirror Units will, with
                           respect to distribution rights and rights upon
                           liquidation, dissolution or winding up of the
                           Partnership, rank (a) senior to the Class A Units and
                           all Partnership Interests ranking junior to the
                           Series C Preferred Mirror Units; (b) on a parity with
                           all Partnership Interests issued by the Partnership
                           the terms of which specifically provide that such
                           Partnership Interests rank on a parity with the
                           Series C Preferred Mirror Units including the
                           Partnership Interests designated as Series A
                           Preferred Mirror Units and Series B Preferred Units;
                           and (c) junior to all Partnership Interests issued by
                           the Partnership the terms of which specifically
                           provide that such Partnership Interests rank senior
                           to the Series C Preferred Mirror Units.

                  (iii)    Distributions.

                           (A)  Pursuant to Section 6.1 of the Partnership
                                Agreement, holders of Series C Preferred Mirror
                                Units shall be entitled to receive, out of funds
                                legally available therefor, cumulative quarterly
                                cash distributions equal to the amount of the
                                cumulative quarterly cash distributions payable
                                on the Series C Preferred Shares. Such
                                distributions shall be payable quarterly in
                                arrears on or before the date on which
                                distributions on the Series B Preferred Shares
                                are payable (each a "Series C Preferred Mirror
                                Unit Distribution Payment Date").

                           (B)  No distributions on Series C Preferred Mirror
                                Units shall be authorized or paid or set apart
                                for payment by the Partnership at such time as
                                the terms and provisions of any agreement of the
                                Partnership, including any agreement relating to
                                its indebtedness, prohibits such authorization,
                                payment or setting apart for payment or provides
                                that such authorization, payment or setting
                                apart for payment would constitute a breach
                                thereof, or a default thereunder, or if such
                                authorization or payment shall be restricted or
                                prohibited by law.

                           (C)  Notwithstanding the foregoing, distributions
                                with respect to the Series C Preferred Mirror
                                Units will accrue whether or not the terms and
                                provisions set forth in Section 1(c)(ii) at any
                                time prohibit the current payment of
                                distributions, whether or not there are funds
                                legally available for such distributions and
                                whether or not such distributions are
                                authorized. Accrued but unpaid distributions on
                                the Series C Preferred Mirror Units will
                                accumulate as of the Series C Preferred Mirror
                                Unit Distribution Payment Date on which they
                                first become payable.

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                           (D)  When distributions are not paid in full (or a
                                sum sufficient for such full payment is not so
                                set apart) upon the Series C Preferred Mirror
                                Units and any other Partnership Interests
                                ranking on a parity as to distributions with the
                                Series C Preferred Mirror Units, including the
                                Series A Preferred Mirror Units and the Series B
                                Preferred Units, all distributions authorized
                                upon the Series C Preferred Mirror Units and any
                                other Partnership Interests ranking on a parity
                                as to distributions with the Series C Preferred
                                Mirror Units shall be authorized pro rata so
                                that the amount of distributions authorized per
                                Partnership Unit of Series C Preferred Mirror
                                Units and such other Partnership Interests shall
                                in all cases bear to each other the same ratio
                                that accrued distributions per Partnership Unit
                                on the Series C Preferred Mirror Units and such
                                other Partnership Interests (which shall not,
                                with respect to such other Partnership
                                Interests, include any accrual in respect of
                                unpaid distributions for prior distribution
                                periods if such other Partnership Interests do
                                not have a cumulative distribution) bear to each
                                other. Any distribution payment or payments on
                                Series C Preferred Mirror Units which may be in
                                arrears shall accrue distributions at the rate
                                of 8.75% per annum.

                           (E)  Except as provided in Section 1(c)(iv), unless
                                full cumulative distributions on the Series C
                                Preferred Mirror Units have been or
                                contemporaneously are authorized and paid or
                                authorized and a sum sufficient for the payment
                                thereof is set apart for payment for all past
                                distribution periods and the then current
                                distribution period, no distributions (other
                                than in Partnership Interests ranking junior to
                                the Series C Preferred Mirror Units as to
                                distributions and upon liquidation, dissolution
                                or winding up) shall be authorized or paid or
                                set aside for payment nor shall any other
                                distribution be authorized or made upon the
                                Class A Units, the Series A Preferred Mirror
                                Units or the Series B Preferred Units or any
                                other Partnership Interests ranking junior to or
                                on a parity with the Series C Preferred Mirror
                                Units as to distributions or upon liquidation,
                                dissolution or winding up, nor shall any Class A
                                Units, Series A Preferred Mirror Units or the
                                Series B Preferred Units or any other
                                Partnership Interests ranking junior to or on a
                                parity with the Series C Preferred Shares as to
                                distributions or upon liquidation be redeemed,
                                purchased or otherwise acquired for any
                                consideration (or any moneys be paid to or made
                                available for a sinking fund for the redemption
                                of any such units or other Partnership
                                Interests) by the Partnership or any other
                                entity controlled directly or indirectly by the
                                Partnership (except by conversion into or
                                exchange for Partnership Interests ranking
                                junior to the Series C Preferred Mirror Units as
                                to distributions and upon liquidation,
                                dissolution or winding up).
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                           (F)  Holders of the Series C Preferred Mirror Units
                                shall not be entitled to any distribution,
                                whether payable in cash, property or Partnership
                                Units in excess of full cumulative distributions
                                on the Series C Preferred Mirror Units as
                                described above. Any distribution payment made
                                on the Series C Preferred Mirror Units shall
                                first be credited against the earliest accrued
                                but unpaid distribution due with respect to such
                                Series C Preferred Mirror Units which remains
                                payable.

                  (iv)     Liquidation Preference.

                           (A)  Upon any voluntary or involuntary liquidation,
                                dissolution or winding up of the affairs of the
                                Partnership, the holders of Series C Preferred
                                Mirror Units then outstanding are entitled to be
                                paid out of the assets of the Partnership
                                available for distribution to the Partners
                                pursuant to Section 13.5(a) of the Partnership
                                Agreement a liquidation preference equal to the
                                Stated Value per Series C Preferred Mirror Unit,
                                plus an amount equal to any accrued and unpaid
                                distributions to the date of payment, before any
                                distribution of assets is made to holders of
                                Class A Units and GP Units or any other
                                Partnership Interests that rank junior to the
                                Series A Preferred Mirror Units upon
                                liquidation, dissolution or winding up.

                           (B)  In the event that, upon any such voluntary or
                                involuntary liquidation, dissolution or winding
                                up, the available assets of the Partnership are
                                insufficient to pay the amount of the
                                liquidating distributions on all outstanding
                                Series C Preferred Mirror Units and the
                                corresponding amounts payable on all other
                                Partnership Interests ranking on a parity with
                                the Series C Preferred Mirror Units in the
                                distribution of assets, including the Series A
                                Preferred Mirror Units and the Series B
                                Preferred Units then such assets shall be
                                allocated among the Series C Preferred Mirror
                                Units, as a class, and each class or series of
                                such other such Partnership Interests, as
                                classes, in proportion to the full liquidating
                                distributions to which they would otherwise be
                                respectively entitled.
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                           (C)  After payment of the full amount of the
                                liquidating distributions to which they are
                                entitled, the holders of Series C Preferred
                                Mirror Units will have no right or claim to any
                                of the remaining assets of the Partnership.

                           (D)  The consolidation or merger of the Partnership
                                with or into any other partnership, corporation,
                                trust or entity or of any other partnership,
                                corporation, trust or other entity with or into
                                the Partnership, or the sale, lease or
                                conveyance of all or substantially all of the
                                property or business of the Partnership, shall
                                not be deemed to constitute a liquidation,
                                dissolution or winding up of the Partnership for
                                purposes of this Section 1(d).

                  (v)      Redemption. In connection with a redemption by the
                           General Partner of any or all of the Series B
                           Preferred Shares, the Partnership shall provide cash
                           to the General Partner for such purpose which shall
                           be equal to the redemption price (including accrued
                           and unpaid distributions) of the Series B Preferred
                           Shares to be redeemed and in exchange one Series C
                           Preferred Mirror Unit shall be canceled with respect
                           to each Series B Preferred Share so redeemed. From
                           and after the date on which the Series B Preferred
                           Shares are redeemed, the Series C Preferred Mirror
                           Units so canceled shall no longer be outstanding and
                           all rights hereunder, to distributions or otherwise,
                           with respect to such Series C Preferred Mirror Units
                           shall cease.

                  (vi)     Conversion. In connection with, and at the time of,
                           the conversion of all or any Series B Preferred
                           Shares into Common Shares, a number of Series B
                           Preferred Mirror Units equal to the number of Series
                           B Preferred Shares so converted shall be converted
                           into a number of Class A Units equal to the number of
                           Common Shares issued upon such conversion.

                  (vii)    Allocations. Allocations of the Partnership's items
                           of income, gain, loss and deduction shall be
                           allocated among holders of Series C Preferred Mirror
                           Units in accordance with Article VII of the
                           Partnership Agreement.

         9. Subparagraph (g) of Section 7.2 of the Partnership Agreement is
amended and restated in its entirety as follows:

                  (i)      Priority Allocation. All or a portion of the Net
                           Income of the Partnership for the Fiscal Year, if
                           any, shall be specially allocated to the Partners
                           holding Series A Preferred Mirror Units, Series B
                           Preferred Units and Series C Preferred Mirror Units
                           in proportion to the cumulative distributions each
                           has received pursuant to Sections 6.1, 6.2, and 13.5


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                           hereof and, with respect to the Partners holding
                           Series A Preferred Mirror Units, Section 1(c) and
                           1(d) of the Fourth Amendment to this Agreement or,
                           with respect to Partners holding Series B Preferred
                           Units, Section 1.C and 1.D of the Fifth Amendment to
                           this Agreement, or, with respect of the Partner
                           holding Series C Preferred Mirror Units, Section 1(c)
                           and 1(d) of the Eighth Amendment to this Agreement
                           from the commencement of the Partnership to the end
                           of such Fiscal Year, in an amount equal to the
                           excess, if any, of the sum of (i) the aggregate Net
                           Loss allocated to such Partners pursuant to Section
                           7.1(b) hereof for all prior Fiscal Years, if any, and
                           (ii) the aggregate distributions received by such
                           Partners pursuant to Sections 6.1, 6.2, and 13.5 of
                           this Agreement and, with respect to Partners holding
                           Series A Preferred Mirror Units, Section 1(c) and
                           1(d) of the Fourth Amendment to this Agreement or,
                           with respect to Partners holding Series B Preferred
                           Units, Section 1.C and 1.D of the Fifth Amendment to
                           this Agreement, or, with respect to Partners holding
                           Series C Preferred Mirror Units, Section 1(c) and
                           1(d) of the Eighth Amendment to this Agreement from
                           the commencement of the Partnership to the end of
                           such Fiscal Year, over the aggregate items of Net
                           Income allocated to such Partners pursuant to this
                           Section 7.2(g) for all prior Fiscal Years.

         10. Except as expressly set forth in this Amendment to the Partnership
Agreement, the Partnership Agreement is hereby ratified and confirmed in each
and every respect.

         IN WITNESS WHEREOF, this Amendment to the Partnership Agreement has
been executed and delivered as of the date first above written.

                                   GENERAL PARTNER:

                                   BRANDYWINE REALTY TRUST

                                   By:
                                       ---------------------------------------
                                   Name: Gerard H. Sweeney
                                   Its:  President and Chief Executive Officer