Document:

EXHIBIT 4.1

                          SUPPLEMENTAL INDENTURE NO. 1

                                 by and between

                         SENIOR HOUSING PROPERTIES TRUST

                                       and

                       STATE STREET BANK AND TRUST COMPANY

                             As of December 20, 2001

           SUPPLEMENTAL TO THE INDENTURE DATED AS OF DECEMBER 20, 2001

                      ------------------------------------

                         SENIOR HOUSING PROPERTIES TRUST

                          8-5/8% Senior Notes due 2012

<PAGE>

         This SUPPLEMENTAL INDENTURE NO. 1 (this "Supplemental  Indenture") made
and entered  into as of December  20, 2001  between  SENIOR  HOUSING  PROPERTIES
TRUST, a Maryland real estate investment trust (the "Company"), and STATE STREET
BANK  AND  TRUST  COMPANY,  a  Massachusetts  trust  company,  as  Trustee  (the
"Trustee"),

                                WITNESSETH THAT:

         WHEREAS,  the Company and the Trustee have  executed  and  delivered an
Indenture, dated as of December 20, 2001 (as amended,  supplemented or otherwise
modified  from  time to time,  the  "Base  Indenture"  and,  together  with this
Supplemental Indenture, as amended, supplemented or otherwise modified from time
to time, the  "Indenture")  to provide for the future  issuance of the Company's
senior debt securities (the  "Securities") to be issued from time to time in one
or more series; and

         WHEREAS,  pursuant  to the  terms of the Base  Indenture,  the  Company
desires to provide for the  establishment  of a series of its Securities,  to be
known as its  8-5/8%  Senior  Notes due  2012,  the form and  substance  of such
Securities and the terms,  provisions and conditions  thereof to be set forth as
provided in the Indenture;

         NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

                                    ARTICLE 1

                                  DEFINED TERMS

         Section 1.1 The following  definitions  supplement,  and, to the extent
inconsistent with, replace the definitions in Section 101 of the Base Indenture:

         "Acquired  Debt"  means Debt of a Person (i)  existing at the time such
Person becomes a Subsidiary or (ii) assumed in connection  with the  acquisition
of assets from such Person, in each case, other than Debt incurred in connection
with,  or in  contemplation  of,  such  Person  becoming  a  Subsidiary  or such
acquisition.  Acquired  Debt shall be deemed to be  incurred  on the date of the
related  acquisition  of assets from any Person or the date the acquired  Person
becomes a Subsidiary.

         "Adjusted Total Assets" is defined in clause (i) of Section 3.1(a).

         "Annual Debt Service" as of any date means the maximum  amount which is
expensed  in any  12-month  period for  interest  on Debt of the Company and its
Subsidiaries  excluding  amortization  of debt  discount and deferred  financing
costs.

         "Business  Day" means any day other than a Saturday  or Sunday or a day
on which banking institutions in the City of New York are required or authorized
to close.

         "Capital  Stock" means,  with respect to any Person,  any capital stock
(including preferred stock), shares, interests, participation or other ownership
interests  (however  designated)  of such

<PAGE>

Person  and  any  rights  (other  than  debt  securities   convertible  into  or
exchangeable for capital stock), warrants or options to purchase any thereof.

         "Cash Equivalents" means:

                  (i) demand  deposits,  certificates  of deposit or  repurchase
         agreements  issued  by or  maintained  with  banks or  other  financial
         institutions;

                  (ii)  marketable  securities  issued  or  directly  and  fully
         guaranteed as to timely  payment by the United States of America or any
         agency or instrumentality thereof, or

                  (iii) any commercial paper or other obligation  rated, at time
         of purchase,  at least "P-2" (or its equivalent) by Moody's or at least
         "A-2" (or its equivalent) by Standard & Poor's.

         "Change of Control" means such time as any "person" or "group" (as such
terms are defined in Sections  13(d) and  14(d)(2) of the Exchange  Act),  other
than an  Excluded  Person,  becomes the  "beneficial  owner" (as defined in Rule
13d-3 under the Exchange  Act) of more than 50% of the total voting power of the
Voting  Stock  of the  Company  on a fully  diluted  basis.  For  such  purpose,
"Excluded  Person" means (i) RMR, HRPT Properties  Trust, a Maryland real estate
investment  trust,   Hospitality   Properties  Trust,  a  Maryland  real  estate
investment  trust,  or any other  entity  for which  financing,  investment  and
operating  oversight  for  substantially  all of  such  entity's  activities  is
provided by RMR, or any successor to or affiliate of such persons,  and (ii) any
person or group  acquiring  shares  issued by the Company in  connection  with a
merger or  acquisition,  if the person or group has agreed  with the  Company to
distribute such shares to the holders of its or their securities within a period
of not longer than one year from the date of such agreement  (the  "Distribution
Period")  and,  giving pro forma effect to such  distribution  as of the date on
which the agreement for the merger or  acquisition  was entered into (and giving
effect to the transactions contemplated by that agreement), no Change of Control
would have occurred;  provided that if such  distribution  does not occur by the
end of the  Distribution  Period,  a Change in  Control  shall be deemed to have
occurred at the end of the Distribution Period.

         "Change  of  Control   Offer"  is  defined  in  Section   4.1  of  this
Supplemental Indenture.

         "Change  of  Control  Payment"  is  defined  in  Section  4.1  of  this
Supplemental Indenture.

         "Change of  Control  Payment  Date" is  defined in Section  4.1 of this
Supplemental Indenture.

         "Consolidated  Income  Available for Debt Service" for any period means
Earnings from Operations of the Company and its Subsidiaries  plus amounts which
have been deducted,  and minus amounts which have been added,  for the following
(without duplication):  (i) interest or distributions on Debt of the Company and
its  Subsidiaries,  (ii) provision for taxes of the Company and its Subsidiaries
based on income,  (iii)  amortization  of debt  discount and deferred  financing
costs,  (iv)  provisions  for  gains  and  losses  on  properties  and  property
depreciation  and  amortization,

                                      -2-
<PAGE>

(v) the  effect of any  noncash  charge  resulting  from a change in  accounting
principles  in  determining  Earnings from  Operations  for such period and (vi)
amortization of deferred charges.

         "Debt" of the Company or any Subsidiary means, without duplication, any
indebtedness  of the Company or any Subsidiary,  whether or not  contingent,  in
respect of (i)  borrowed  money or  evidenced  by bonds,  notes,  debentures  or
similar  instruments,  (ii)  indebtedness  for  borrowed  money  secured  by any
Encumbrance existing on property owned by the Company or any Subsidiary,  to the
extent of the  lesser of (x) the  amount of  indebtedness  so secured or (y) the
fair  market  value of the  property  subject  to such  Encumbrance,  (iii)  the
reimbursement  obligations,  contingent  or otherwise,  in  connection  with any
letters of credit  actually  issued  (other  than  letters  of credit  issued to
provide credit  enhancement or support with respect to other indebtedness of the
Company or any  Subsidiary  otherwise  reflected as Debt  hereunder)  or amounts
representing  the  balance  deferred  and  unpaid of the  purchase  price of any
property  or  services,  except any such  balance  that  constitutes  an accrued
expense,  trade payable,  conditional sale obligations or obligations  under any
title retention  agreement,  (iv) the principal amount of all obligations of the
Company  or any  Subsidiary  with  respect  to  redemption,  repayment  or other
repurchase  of any  Disqualified  Stock,  or (v) any  lease of  property  by the
Company  or any  Subsidiary  as  lessee  which  is  reflected  on the  Company's
consolidated  balance sheet as a capitalized  lease in accordance  with GAAP, to
the extent, in the case of items of indebtedness  under (i) through (iii) above,
that any such items (other than  letters of credit)  would appear as a liability
on the Company's  consolidated  balance sheet in accordance with GAAP. Debt also
includes, to the extent not otherwise included, any obligation by the Company or
any  Subsidiary to be liable for, or to pay, as obligor,  guarantor or otherwise
(other than for purposes of collection in the ordinary course of business), Debt
of  another  Person  (other  than  the  Company  or any  Subsidiary);  it  being
understood  that Debt  shall be  deemed to be  incurred  by the  Company  or any
Subsidiary  whenever  the  Company  or such  Subsidiary  shall  create,  assume,
guarantee or otherwise become liable in respect thereof.

         "Disqualified  Stock"  means,  with respect to any Person,  any Capital
Stock of such Person which by the terms of such  Capital  Stock (or by the terms
of any security into which it is convertible or for which it is  exchangeable or
exercisable),  upon the happening of any event or otherwise (other than pursuant
to a change of control  provision not  materially  more  favorable to the holder
thereof than that set forth in Section 4.1 of this Supplemental Indenture),  (i)
matures or is mandatorily  redeemable,  pursuant to a sinking fund obligation or
otherwise  (other than Capital Stock which is redeemable  solely in exchange for
Capital Stock which is not Disqualified Stock or for Subordinated Debt), (ii) is
convertible   into  or  exchangeable   or  exercisable  for  Debt,   other  than
Subordinated Debt or Disqualified Stock, or (iii) is redeemable at the option of
the holder  thereof,  in whole or in part  (other  than  Capital  Stock which is
redeemable solely in exchange for Capital Stock which is not Disqualified  Stock
or for  Subordinated  Debt);  in each case on or prior to the stated maturity of
the Notes.

         "Earnings from Operations" for any period means net earnings  excluding
gains and losses on sales of investments,  extraordinary items, distributions on
equity  securities and property  valuation losses, as reflected in the financial
statements of the Company and its Subsidiaries for such period,  determined on a
consolidated basis in accordance with GAAP.

                                      -3-
<PAGE>

         "Encumbrance"  means  any  mortgage,  lien,  charge,  pledge,  security
interest or other encumbrance of any kind.

         "Exchange Act" means the Securities Exchange Act of 1934, as amended.

         "Excluded  Refunding"  means,  at any time,  any  voluntary or optional
principal payment, or voluntary or optional redemption,  repurchase, defeasance,
or other  acquisition  or  retirement  for value,  of  Subordinated  Debt of the
Company or any  Subsidiary  in an amount not  exceeding  the  aggregate Net Cash
Proceeds  received by the Company and its  Subsidiaries  from the  substantially
concurrent sale of Qualified Subordinated Debt, to the extent such proceeds have
not  theretofore  been taken in account in calculating the amount of an Excluded
Refunding.  For such purpose,  "Qualified  Subordinated Debt" means Subordinated
Debt  of  the  Company  or a  Subsidiary  of the  Company  (or  trust  preferred
securities  or similar  Capital Stock of a Subsidiary of the Company as to which
any  related  Debt of the  Company  or  other  Subsidiaries  of the  Company  is
Subordinated  Debt)  which  does not  mature  and is not  subject  to  mandatory
repurchase  or  redemption  or to  repurchase or redemption at the option of the
holder  thereof  (other  than  pursuant  to a change of  control  provision  not
materially  more  favorable to the holder thereof than that set forth in Section
4.1 of this  Supplemental  Indenture)  in whole or in part  prior to the  stated
maturity of the Notes.

         "Funds from  Operations"  for any period means Earnings from Operations
for such period plus amounts  which have been  deducted,  and minus amounts that
have been added,  for the  following  (without  duplication):  (i) provision for
taxes of the Company and its Subsidiaries based on income,  (ii) amortization of
debt  discount and deferred  financing  costs,  (iii)  provisions  for gains and
losses on properties and property depreciation and amortization, (iv) the effect
of any  noncash  charge  resulting  from a change in  accounting  principles  in
determining  Earnings from Operations for such period,  (v) expenses and charges
relating to the spin-off of Five Star Quality Care, Inc., and (vi)  amortization
of deferred charges.

         "Interest Payment Date" with respect to the Notes is defined in Section
101 of the Base Indenture and Section 2.1(b) of this Supplemental Indenture.

         "Make-Whole  Amount" means, in connection with any optional  redemption
or accelerated payment of the Notes, the excess, if any, of:

         (i)      the aggregate  present value as of the date of such redemption
                  or  accelerated  payment  of each  dollar of  principal  being
                  redeemed  or paid and the  amount of  interest  (exclusive  of
                  interest  accrued  to the date of  redemption  or  accelerated
                  payment)  that would have been payable in respect of each such
                  dollar if such redemption or accelerated  payment had not been
                  made, determined by discounting,  on a semi-annual basis, such
                  principal and interest at the Reinvestment Rate (determined on
                  the  third  Business  Day  preceding  the  date  a  notice  of
                  redemption is given or  declaration of  acceleration  is made)
                  from the respective dates on which such principal and interest
                  would have been payable if such  redemption or payment had not
                  been made, over

                                      -4-
<PAGE>

         (ii)     the aggregate  Outstanding principal amount of the Notes being
                  redeemed or paid.

         "Moody's"  means  Moody's  Investors  Services,  Inc. or any  successor
thereof.

         "Net Cash  Proceeds"  means the  proceeds  of any  issuance  or sale of
Capital Stock, in the form of cash or Cash  Equivalents,  including  payments in
respect of deferred payment  obligations when received in the form of, or shares
or other  assets when  disposed  for,  cash or Cash  Equivalents  (except to the
extent that such  obligations  are financed or sold with recourse to the Company
or any  Subsidiary),  net of attorney's fees,  accountant's  fees and brokerage,
consultation,  underwriting  and other fees and  expenses  actually  incurred in
connection  with such  issuance  or sale and net of taxes  paid or  payable as a
result thereof.

         "Notes" means the Company's 8-5/8% Senior Notes due 2012,  issued under
the Indenture.

         "Regular  Record  Date" with respect to the Notes is defined in Section
101 of the Base Indenture and Section 2.1(b) of this Supplemental Indenture.

         "Reinvestment  Rate" means 0.50% plus the arithmetic mean of the yields
under  the  respective   heading  Week  Ending  published  in  the  most  recent
Statistical  Release  under the caption  Treasury  Constant  Maturities  for the
maturity  (rounded to the nearest month)  corresponding to the remaining life to
maturity, as of the date of the principal being redeemed or paid. If no maturity
exactly  corresponds to such maturity,  yields for the two published  maturities
most closely  corresponding to such maturity shall be calculated pursuant to the
immediately  preceding  sentence and the Reinvestment Rate shall be interpolated
or extrapolated from such yields on a straight-line  basis,  rounding in each of
such relevant  periods to the nearest month.  For the purpose of calculating the
Reinvestment  Rate, the most recent  Statistical  Release published prior to the
date of determination of the Make-Whole Amount shall be used.

         "RMR"  means  Reit  Management  &  Research  LLC,  a  Delaware  limited
liability company.

         "Secured Debt" means Debt secured by any Encumbrance.

         "Standard & Poor's" means Standard & Poor's Rating Services, a division
of The McGraw-Hill Companies, Inc. or any successor thereof.

         "Statistical   Release"  means  that  statistical   release  designated
H.15(519) or any successor  publication  that is published weekly by the Federal
Reserve  System and that  establishes  annual  yields on actively  traded United
States  government  securities  adjusted  to  constant  maturities,  or, if such
statistical  release is not published at the time of any determination under the
Indenture, then such other reasonably comparable index we designate.

         "Subordinated  Debt"  means  Debt  which by the  terms of such  Debt is
subordinated  in right of payment to the  principal of and interest and premium,
if any, on the Notes.

         "Subsidiary"  means any corporation or other entity of which a majority
of (i) the voting power of the voting equity  securities or (ii) the outstanding
equity interests of which are owned,

                                      -5-
<PAGE>

directly or indirectly,  by the Company or one or more other Subsidiaries of the
Company.  For the purposes of this definition,  "voting equity securities" means
equity  securities  having voting power for the election of directors or similar
functionaries,  whether  at all  times  or only so long as no  senior  class  of
security has such voting power by reason of any contingency.

         "Total  Assets" as of any date  means the sum of (i) the  Undepreciated
Real Estate Assets and (ii) all other assets of the Company and its Subsidiaries
determined  in  accordance  with GAAP (but  excluding  accounts  receivable  and
intangibles).

         "Total Unencumbered Assets" means the sum of (i) the Undepreciated Real
Estate  Assets of the Company and its  Subsidiaries  not securing any portion of
Secured  Debt and (ii) all  other  assets,  including  accounts  receivable  and
intangibles,  of the Company and its  Subsidiaries  not  securing any portion of
Secured Debt  determined on a  consolidated  basis in  accordance  with GAAP. If
Secured Debt  secured by real estate or other  property or assets of the Company
or its  Subsidiaries  ("Secondary  Collateral")  is fully defeased in accordance
with the terms  thereof  or is also  secured by cash or Cash  Equivalents  in an
amount  (determined at the lesser of (i) carrying value in accordance  with GAAP
or (ii) fair market value) at least equal to the outstanding principal amount of
such Secured Debt, such Secondary  Collateral  shall be deemed not to secure any
portion of such Secured Debt for purposes of this definition.

         "Undepreciated  Real  Estate  Assets"  as of any  date  means  the cost
(original cost plus capital  improvements  less adjustments to carrying value in
accordance  with  GAAP  made  prior  to  January  1,  2001) of real  estate  and
associated  tangible  personal  property used in connection with the real estate
assets of the Company and its Subsidiaries on such date, before depreciation and
amortization determined on a consolidated basis in accordance with GAAP.

         "Unsecured Debt" means any Debt which is not Secured Debt.

         "Voting  Stock" of any Person  means the  Capital  Stock of such Person
that is at the time  entitled to vote in the election of the board of directors,
board of trustees or the equivalent of such Person.

                                    ARTICLE 2

                               TERMS OF THE NOTES

         Section 2.1 Pursuant to Section 301 of the  Indenture,  the Notes shall
have the following terms and conditions:

         (a) Title;  Aggregate  Principal Amount; Form of Notes. The Notes shall
be Registered Securities under the Indenture and shall be known as the Company's
"8-5/8%  Senior  Notes due 2012."  The Notes  will be  limited  to an  aggregate
principal amount of $200,000,000,  subject to the right of the Company to reopen
such series for issuances of additional securities of such series and except (i)
as provided in this Section and (ii) for Securities  authenticated and delivered
upon  registration  of  transfer  of, or in exchange  for, or in lieu of,  other
Securities  of the series  pursuant to Section 304, 305, 306, 906 or 1107 of the
Indenture and except for any  Securities  which,  pursuant to Section 303 of the
Indenture,  are deemed never to have been authenticated

                                      -6-
<PAGE>

and delivered hereunder.  The Notes (together with the Trustee's  certificate of
authentication) shall be substantially in the form of Exhibit A hereto, which is
hereby incorporated in and made a part of this Supplemental Indenture.

         The Notes will be issued in the form of one or more  registered  global
securities  without coupons  ("Global Notes") that will be deposited with, or on
behalf of, The Depository Trust Company  ("DTC"),  and registered in the name of
DTC's nominee,  Cede & Co. Except under the  circumstance  described  below, the
Notes will not be issuable in definitive form.  Unless and until it is exchanged
in whole or in part for the individual notes represented  thereby, a Global Note
may not be  transferred  except  as a whole by DTC to a  nominee  of DTC or by a
nominee of DTC to DTC or another  nominee of DTC or by DTC or any nominee of DTC
to a successor depositary or any nominee of such successor.

         So long as DTC or its nominee is the registered owner of a Global Note,
DTC or such nominee,  as the case may be, will be  considered  the sole owner or
holder of the Notes  represented by such Global Note for all purposes under this
Supplemental Indenture. Except as described below, owners of beneficial interest
in Notes  evidenced  by a Global  Note will not be  entitled  to have any of the
individual Notes represented by such Global Note registered in their names, will
not  receive or be entitled  to receive  physical  delivery of any such Notes in
definitive  form and will not be considered the owners or holders  thereof under
the Indenture or this Supplemental Indenture.

         If DTC is at any time  unwilling,  unable or  ineligible to continue as
depositary and a successor  depositary is not appointed by the Company within 90
days, the Company will issue individual Notes in exchange for the Global Note or
Global Notes  representing such Notes. In addition,  the Company may at any time
and in its sole  discretion,  subject  to certain  limitations  set forth in the
Indenture,  determine not to have any of such Notes  represented  by one or more
Global Notes and, in such event, will issue individual Notes in exchange for the
Global Note or Global Notes  representing the Notes.  Individual Notes so issued
will be issued in denominations of $1,000 and integral multiples thereof.

         (b) Interest and Interest  Rate. The Notes will bear interest at a rate
of 8-5/8% per annum,  from  December  20, 2001 (or, in the case of Notes  issued
upon the  reopening  of this series of Notes,  from the date  designated  by the
Company in connection  with such  reopening) or from the  immediately  preceding
Interest  Payment  Date to which  interest has been paid or duly  provided  for,
payable  semiannually  on each January 15 and July 15,  commencing July 15, 2002
(each of which shall be an  "Interest  Payment  Date"),  to the Persons in whose
names the Notes are registered in the Security Register at the close of business
on January 1 and July 1, as the case may be  (whether  or not a  Business  Day),
next preceding such Interest Payment Date (each, a "Regular Record Date").

         (c) Principal Repayment;  Currency. The stated maturity of the Notes is
January 15, 2012,  provided,  however,  the Notes may be earlier redeemed at the
option of the Company as provided in paragraph (d) below.  The principal of each
Note  payable  on its  maturity  date  shall be paid  against  presentation  and
surrender  thereof  at  the  Corporate  Trust  Office  of the  Trustee,  located
initially at Two Avenue de Lafayette,  Boston, Massachusetts 02111, in such coin

                                      -7-
<PAGE>

or currency  of the United  States of America as at the time of payment is legal
tender for the payment of public or private debts.

         (d) Redemption at the Option of the Company.  The Notes will be subject
to  redemption  at any time at the option of the  Company,  in whole or in part,
upon not less than 30 nor more than 60 days'  notice to each  Holder of Notes to
be redeemed at its address appearing in the Security Register,  at a price equal
to the sum of (i) the Outstanding  principal amount of the Notes being redeemed,
plus accrued and unpaid  interest to but  excluding  the  applicable  Redemption
Date, plus (ii) the Make-Whole Amount, if any.

         (e) Notices. All notices and other communications hereunder shall be in
writing and shall be deemed to have been duly given if mailed or  transmitted by
any standard form of telecommunication. Notices to the Company shall be directed
to it at 400 Centre Street, Newton,  Massachusetts 02458, Attention:  President;
notices to the  Trustee  shall be  directed  to it at Two  Avenue de  Lafayette,
Boston,  Massachusetts 02111, Attention:  Corporate Trust Department, Re: Senior
Housing Properties Trust 8-5/8% Senior Notes due 2012; or as to either party, at
such other address as shall be  designated by such party in a written  notice to
the other party.

         (f) Global  Note  Legend.  Each  Global  Note shall bear the  following
legend on the face thereof:

         UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
         THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO ISSUER
         OR ITS AGENT FOR REGISTRATION OF TRANSFER,  EXCHANGE,  OR PAYMENT,  AND
         ANY  CERTIFICATE  ISSUED IS  REGISTERED IN THE NAME OF CEDE & CO. OR IN
         SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED  REPRESENTATIVE OF DTC
         (AND ANY  PAYMENT IS MADE TO CEDE & CO. OR TO SUCH  OTHER  ENTITY AS IS
         REQUESTED  BY AN  AUTHORIZED  REPRESENTATIVE  OF  DTC),  ANY  TRANSFER,
         PLEDGE,  OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON
         IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN
         INTEREST HEREIN.

         (g)  Applicability  of Discharge,  Defeasance  and Covenant  Defeasance
Provisions.  The  Discharge,  Defeasance and Covenant  Defeasance  provisions in
Article Thirteen of the Indenture will apply to the Notes.

                                    ARTICLE 3

                              ADDITIONAL COVENANTS

         Section  3.1  Holders  of the  Notes  shall  have  the  benefit  of the
following  covenants,  in addition to the  covenants of the Company set forth in
Article Eight of the Indenture:

         (a)  Limitations on Incurrence of Debt.

                                      -8-
<PAGE>

                  (i) The Company will not,  and will not permit any  Subsidiary
         to,  incur  any  Debt  if,  immediately  after  giving  effect  to  the
         incurrence of such  additional Debt and the application of the proceeds
         thereof,  the aggregate principal amount of all outstanding Debt of the
         Company and its  Subsidiaries  on a  consolidated  basis  determined in
         accordance  with GAAP is greater than 60% of the sum  ("Adjusted  Total
         Assets") of (without  duplication)  (A) the Total Assets of the Company
         and its  Subsidiaries as of the end of the calendar  quarter covered in
         the Company's  Annual Report on Form 10-K, or Quarterly  Report on Form
         10-Q, as the case may be, most recently  filed with the  Securities and
         Exchange  Commission  (or,  if such filing is not  permitted  under the
         Exchange  Act  with  the  Trustee)  prior  to the  incurrence  of  such
         additional Debt and (B) the purchase price of any real estate assets or
         mortgages  receivable  acquired,  and  the  amount  of  any  securities
         offering  proceeds  received (to the extent that such proceeds were not
         used to acquire real estate  assets or mortgages  receivable or used to
         reduce Debt),  by the Company or any  Subsidiary  since the end of such
         calendar quarter,  including those proceeds obtained in connection with
         the incurrence of such additional Debt.

                  (ii) The Company will not, and will not permit any  Subsidiary
         to, incur any Secured Debt if,  immediately  after giving effect to the
         incurrence of such  additional  Secured Debt and the application of the
         proceeds  thereof,  the aggregate  principal  amount of all outstanding
         Secured  Debt of the Company  and its  Subsidiaries  on a  consolidated
         basis is greater than 40% of Adjusted Total Assets.

                  (iii) The Company will not, and will not permit any Subsidiary
         to, incur any Debt if the ratio of  Consolidated  Income  Available for
         Debt Service to the Annual Debt Service for the four consecutive fiscal
         quarters most recently ended prior to the date on which such additional
         Debt is to be  incurred  shall have been less than 2.0 to 1.0, on a pro
         forma basis after giving effect  thereto and to the  application of the
         proceeds therefrom, and calculated on the assumption that (A) such Debt
         and any other Debt  incurred by the Company and its  Subsidiaries  on a
         consolidated basis since the first day of such four-quarter  period and
         the application of the proceeds therefrom, including to refinance other
         Debt,  had occurred at the beginning of such period;  (B) the repayment
         or  retirement  of any other Debt by the Company  and its  Subsidiaries
         since the first date of such  four-quarter  period  had been  repaid or
         retired at the  beginning of such period  (except  that, in making such
         computation,  the amount of Debt under any  revolving  credit  facility
         shall be  computed  based upon the average  daily  balance of such Debt
         during such period);  (C) in the case of Acquired Debt or Debt incurred
         in  connection  with  any  acquisition  since  the  first  day of  such
         four-quarter  period,  the related  acquisition  had occurred as of the
         first day of such period with  appropriate  adjustments with respect to
         such acquisition being included in such pro forma calculation;  and (D)
         in the case of any  acquisition  or  disposition  by the Company or its
         Subsidiaries  on a  consolidated  basis of any asset or group of assets
         since the first day of such  four-quarter  period,  whether  by merger,
         stock purchase or sale, or asset purchase or sale, such  acquisition or
         disposition  or any related  repayment  of Debt had  occurred as of the
         first day of such period with the appropriate  adjustments with respect
         to such  acquisition  or  disposition  being included in such pro forma
         calculation.  If the Debt giving rise to the need to make the foregoing
         calculation  or any  other  Debt  incurred  after  the first day of the
         relevant  four-quarter  period bears

                                      -9-
<PAGE>

         interest  at a floating  rate then,  for  purposes of  calculating  the
         Annual Debt  Service,  the interest rate on such Debt shall be computed
         on a pro forma basis as if the average  interest  rate which would have
         been in effect during the entire such four-quarter  period had been the
         applicable rate for the entire such period.

         (b)  Limitations on  Distributions.  The Company will not, and will not
permit  any  Subsidiary  to,  (i)  declare  or pay  any  dividend  or  make  any
distribution  on or with respect to the Company's  Capital Stock (other than (x)
dividends or  distributions  payable  solely in shares of the Company's  Capital
Stock, other than Disqualified Stock, or in options, warrants or other rights to
acquire  shares of such Capital Stock and (y) the spin-off  distribution  of the
Capital Stock of Five Star Quality Care, Inc.); (ii) purchase, redeem, retire or
otherwise  acquire for value any shares of the Company's Capital Stock; or (iii)
make any  voluntary  or optional  principal  payment,  or  voluntary or optional
redemption,  repurchase,  defeasance,  or other  acquisition  or retirement  for
value,  of  Subordinated   Debt  (other  than  Excluded   Refundings);   unless,
immediately  after  giving  pro  forma  effect  to such  distribution  (each,  a
"Restricted Payment"):

         (A)      no Default  under the  Indenture  shall have  occurred  and be
                  continuing  or  would  occur as a  result  of such  Restricted
                  Payment;

         (B)      the Company and its Subsidiaries  would have been permitted to
                  incur at least  $1.00 of  additional  Debt  (other  than  Debt
                  between  the  Company  and one or  more  its  Subsidiaries  or
                  between  one or more  its  Subsidiaries)  under  the  terms of
                  Section 3.1(a) of this Supplemental Indenture; and

         (C)      the aggregate  amount of all Restricted  Payments (the amount,
                  if other than in cash,  to be  determined in good faith by the
                  Board, whose  determination  shall be conclusive and evidenced
                  by  a  Board   Resolution)   made   after  the  date  of  this
                  Supplemental Indenture would not exceed the sum of:

                  (I)      95% of Funds from Operations  accrued on a cumulative
                           basis  during  the  period  (taken as one  accounting
                           period)  beginning  on  October 1, 2001 and ending on
                           the last day of the Company's most recently completed
                           calendar quarter; plus

                  (II)     100% of the aggregate  Net Cash Proceeds  received by
                           the  Company  after  the  date of  this  Supplemental
                           Indenture  from the issuance or sale of Capital Stock
                           of the Company to a Person  which is not a Subsidiary
                           of the Company; plus

                  (III)    $15,000,000.

Notwithstanding the foregoing,  this Section 3.1(b) shall not prohibit or limit,
and shall not be violated  by, (i) any  dividend,  distribution  or other action
which is necessary to distribute  100% of the Company's  real estate  investment
trust taxable income  (determined prior to any deductions for dividends paid) or
to maintain the  Company's  status as a real estate  investment  trust under the
Internal Revenue Code of 1986, as amended,  if the aggregate principal amount of
all outstanding Debt of the Company and its Subsidiaries on a consolidated basis
determined in

                                      -10-
<PAGE>

accordance  with GAAP is less than 60% of  Adjusted  Total  Assets,  or (ii) the
payment of any dividend or other distribution  within 60 days of the declaration
thereof if at the date of  declaration  thereof such payment would have complied
with the provisions of this Section 3.1(b).

         (c)  Maintenance  of Total  Unencumbered  Assets.  The  Company and its
Subsidiaries  will maintain at all times Total  Unencumbered  Assets of not less
than 150% of the aggregate outstanding principal amount of the Unsecured Debt of
the Company and its  Subsidiaries  on a  consolidated  basis in accordance  with
GAAP.

         (d) Company May  Consolidate,  Etc., Only on Certain Terms. In addition
to the  provisions  of  Section  801 of the  Indenture,  the  Company  shall not
consolidate with or merge into any other Person or convey, transfer or lease its
properties  and assets  substantially  as an  entirety  to any  Person,  and the
Company  shall not  permit  any  Person to  consolidate  with or merge  into the
Company or convey,  transfer or lease its properties and assets substantially as
an entirety to the  Company,  unless  immediately  after  giving  effect to such
transaction,  the Person formed by such  consolidation or into which the Company
is merged or the Person  which  acquires by  conveyance  or  transfer,  or which
leases,  the properties and assets of the Company  substantially  as an entirety
would be permitted to incur at least $1.00 of  additional  Debt (other than Debt
between such Person and one or more of its  Subsidiaries  or between one or more
or its  Subsidiaries)  under the terms of  Section  3.1(a) of this  Supplemental
Indenture.

                                    ARTICLE 4

                   OFFER TO REPURCHASE UPON CHANGE OF CONTROL

         Section 4.1 Subject to Section 4.2, if a Change of Control occurs,  the
Company shall make an offer (a "Change of Control  Offer") to each Holder of the
Notes to  repurchase  all or any part (equal to $1,000 or an  integral  multiple
thereof) of such Holder's Notes at a purchase price,  in cash,  equal to 101% of
the  aggregate  outstanding  principal  amount  of the Notes  repurchased,  plus
accrued and unpaid interest thereon,  if any (subject to the right of Holders on
the  relevant  record  date to receive  interest  due on the  relevant  interest
payment date), to the date of purchase (the "Change of Control Payment").

         Within 10 days following any Change of Control,  the Company shall mail
a written  offer (an  "Offer")  to each Holder in  accordance  with the terms of
Section 1104 of the Base Indenture.  The Offer shall contain all the information
required by applicable law to be included therein.  The Offer shall also contain
information  concerning the business of the Company and its  Subsidiaries  which
the Company in good faith  believes will enable such Holders to make an informed
decision  with respect to the Change of Control  Offer.  The Offer shall contain
all instructions and materials  necessary to enable such Holders to tender Notes
pursuant to the Change of Control Offer. The Offer shall also state:

         (a) that the Change of Control  Offer is being  made  pursuant  to this
covenant and that all Notes  tendered will be accepted for payment on the Change
of Control Payment Date, as defined below;

                                      -11-
<PAGE>

         (b) the purchase price and the purchase date, which shall be no earlier
than 30 days and no later than 60 days from the date such  notice is mailed (the
"Change of Control Payment  Date"),  which date shall also be the date the Offer
expires;

         (c)  that any Note not tendered will continue to accrue interest;

         (d) that,  unless the Company  defaults in the payment of the Change of
Control  Payment,  all Notes  accepted  for  payment  pursuant  to the Change of
Control Offer shall cease to accrue interest after the Change of Control Payment
Date;

         (e) that  Holders  electing to have any Notes  purchased  pursuant to a
Change of Control Offer will be required to surrender  the Notes,  with the form
entitled  "Option  of  Holder to Elect  Purchase"  on the  reverse  of the Notes
completed,  to the Paying Agent at the address  specified in the notice prior to
close of  business  on the date  specified  in such  notice,  which shall not be
earlier than first to occur of (i) the  thirtieth day following the date of such
notice and (ii) the third  Business Day preceding the Change of Control  Payment
Date;

         (f) that  Holders  will be entitled to withdraw  their  election if the
Paying  Agent  receives,  not later  than the close of  business  on the  second
Business Day  preceding the Change of Control  Payment Date, a telegram,  telex,
facsimile  transmission  or letter  setting  forth the name of the  Holder,  the
principal  amount of Notes  delivered  for purchase,  and a statement  that such
Holder is withdrawing its election to have the Notes purchased;

         (g) that Holders whose Notes are being  purchased  only in part will be
issued new Notes equal in  principal  amount to the  unpurchased  portion of the
Notes  surrendered,  which  unpurchased  portion  must be  equal  to  $1,000  in
principal amount or an integral multiple thereof; and

         (h) that Holders electing to have a Note purchased pursuant to a Change
of Control  Offer may elect to have Notes  purchased  in integral  multiples  of
$1,000 only.

         On the Change of Control Payment Date, the Company shall, to the extent
lawful,

                  (i)  accept for  payment  all Notes or  portions  of the Notes
         properly tendered pursuant to the Change of Control Offer;

                  (ii)  deposit  with the  Paying  Agent an amount  equal to the
         Change of Control  Payment in respect of all Notes or  portions  of the
         Notes so tendered; and

                  (iii)  deliver or cause to be  delivered  to the  Trustee  the
         Notes so accepted  together with an Officers'  Certificate  stating the
         aggregate principal amount of Notes or portions thereof being purchased
         by the Company.

         The Paying Agent shall  promptly mail to each Holder of Notes  properly
tendered  payment  in an amount  equal to the  Change of  Control  Payment  with
respect to the purchased Notes, and the Trustee shall promptly  authenticate and
mail (or cause to be  transferred by book

                                      -12-
<PAGE>

entry) to each Holder a new Note equal in  principal  amount to any  unpurchased
portion of the Notes surrendered by such Holder, if any; provided, however, that
each such new Note  shall be in a  principal  amount  of  $1,000 or an  integral
multiple thereof.  The Company shall publicly announce the results of the Change
of  Control  Offer on or as soon as  practicable  after the  Change  of  Control
Payment Date.

         The Change of Control  provisions  described  above shall be applicable
whether or not any other provisions of this Indenture are applicable.

         The Company shall comply with the  requirements of Section 14(e) of the
Exchange Act and any other  securities  laws or  regulations to the extent those
laws and  regulations  are  applicable  to any Change of Control  Offer.  If the
provisions of any of the applicable  securities  laws or securities  regulations
conflict with the  provisions of this Section 4.1, the Company shall comply with
the applicable  securities  laws and regulations and shall not be deemed to have
breached its obligations under this Section 4.1 by virtue of the compliance.

         Notwithstanding  the  foregoing  provisions  of this  Section  4.1, the
Company  shall not be  required  to make or give  notice of a Change of  Control
Offer and, if made or given,  shall not be required to  repurchase  Notes on the
related  Change of  Control  Payment  Date if,  prior to the date on which  such
notice or Change of Control Offer is required to be given or made or such Change
of Control Payment Date, as applicable

                  (i) the Company shall have irrevocably exercised its option to
         redeem  the  Notes  in  whole   pursuant  to  Section  2.1(d)  of  this
         Supplemental  Indenture;  provided that if the Company shall default in
         its obligation to redeem the Notes  pursuant to such  redemption on the
         applicable  Redemption  Date,  the Company  shall  become  obligated to
         commence a Change of Control Offer in accordance with this Article 4 on
         such Redemption Date; or

                  (ii)  giving  effect to the  related  Change of  Control,  the
         Moody's and Standard & Poor's shall have  confirmed  that the Notes are
         rated  "Ba3"  (or its  equivalent)  or  higher  and  "BB-"  or  higher,
         respectively.

         The Company  shall not be  required  to make a Change of Control  Offer
upon a Change of Control if a third party  makes the Change of Control  Offer in
the manner,  at the times and otherwise in compliance with the  requirements set
forth in this  Indenture  applicable  to a Change of  Control  Offer made by the
Company and purchases all Notes properly  tendered and not withdrawn  under such
Change of Control Offer.

         The provisions of the Indenture relating to the Company's obligation to
make an offer  to  repurchase  the  Notes as a  result  of a Change  of  Control
(including  this  Article  4 and  clause  (a) of  Section  5.1) may be waived or
modified  with the consent of the  Holders of at least a majority  in  principal
amount of the Notes then outstanding.

         Section 4.2. The provisions of Section 4.1 shall terminate and cease to
have  further  force or effect on or after the first date,  if any, on which the
Notes shall have been rated "Baa3" (or its  equivalent) or higher by Moody's and
"BBB-" (or its

                                      -13-
<PAGE>

equivalent) or higher by Standard & Poor's.

                                    ARTICLE 5

                          ADDITIONAL EVENTS OF DEFAULT

         Section 5.1 For purposes of this Supplemental  Indenture and the Notes,
in addition to the Events of Default set forth in Section 501 of the  Indenture,
it shall also  constitute  an "Event of Default"  if (a) the Company  shall have
failed to consummate a Change of Control Offer in accordance with the provisions
of Article 4 of this Supplemental  Indenture, or (b) one or more final judgments
or orders (not covered by insurance, treating any deductibles, self-insurance or
retention as not so covered)  for the payment of money in excess of  $10,000,000
in the  aggregate  for all such  judgments or orders  against the Company or any
Subsidiary  and such  judgments or orders shall not be paid or  discharged,  and
there shall be a period of 60 consecutive days after the final judgment or order
that causes such aggregate amount to exceed  $10,000,000  million during which a
stay of enforcement of such final judgment(s) or order(s) are not in effect.

         Section  5.2  Notwithstanding  any  provisions  to the  contrary in the
Indenture including, without limitation,  Section 501(a) thereof, the failure to
pay  the  principal  of or any  premium  on the  Notes  at  its  Maturity  shall
constitute an "Event of Default".

         Section  5.3  Notwithstanding  any  provisions  to the  contrary in the
Indenture  including,  without limitation,  Section 501(e) thereof,  the default
under any bonds,  debentures,  notes or other  evidences of  indebtedness of the
Company,  or under any  mortgage,  indenture or other  instrument of the Company
(including  a default with  respect to  Securities  of any series other than the
Notes)  under  which  there may be issued or by which  there may be secured  any
indebtedness  of the Company (or by one or more  Subsidiaries,  the repayment of
which  the  Company  has  guaranteed  or  for  which  the  Company  is  directly
responsible or liable as obligor or guarantor),  whether such  indebtedness  now
exists or shall  hereafter  be created,  which  default(s)  shall  constitute  a
failure to pay an  aggregate  principal  amount  exceeding  $10,000,000  of such
indebtedness  when due and payable after the expiration of any applicable  grace
period with respect  thereto and shall have resulted in such  indebtedness in an
aggregate principal amount exceeding  $10,000,000 becoming or being declared due
and payable  prior to the date on which it would  otherwise  have become due and
payable, without such indebtedness having been discharged,  or such acceleration
having been rescinded or annulled,  within a period of 10 days after there shall
have been given,  by registered or certified mail, to the Company by the Trustee
or to the  Company  and the  Trustee by the  Holders  of at least a majority  in
principal  amount of the  Outstanding  Notes a written  notice  specifying  such
default and requiring the Company to cause such indebtedness to be discharged or
cause such acceleration to be rescinded or annulled and stating that such notice
is a "Notice of Default" hereunder, shall constitute an Event of Default.

         Section  5.4.  Notwithstanding  any  provisions  to the contrary in the
Indenture,  upon the acceleration of the Notes in accordance with Section 502 of
the Indenture,  the amount

                                      -14-
<PAGE>

immediately  due and payable in respect of the Notes shall equal the Outstanding
principal amount thereof, plus accrued and unpaid interest,  plus the Make Whole
Amount.

                                    ARTICLE 6

                                  EFFECTIVENESS

         Section 6.1 This  Supplemental  Indenture  shall be  effective  for all
purposes as of the date and time this  Supplemental  Indenture has been executed
and delivered by the Company and the Trustee in accordance  with Article Nine of
the Indenture.  As  supplemented  hereby,  the Indenture is hereby  confirmed as
being in full force and effect.

                                    ARTICLE 7

                                NOTICE TO TRUSTEE
         Section 7.1  Notwithstanding  anything to the contrary in the Indenture
including,  without  limitation,  Section 1102 thereof,  in connection  with the
redemption  at the  election  of the  Company  of less than all the  Notes,  the
Company shall notify the Trustee of the  establishment  of a Redemption Date and
the  principal  amount of Notes to be  redeemed  at least 45 days  prior to such
Redemption Date unless a shorter period shall be satisfactory to the Trustee.

                                    ARTICLE 8

                                  MISCELLANEOUS

         Section 8.1 In the event any provision of this  Supplemental  Indenture
shall be held invalid or unenforceable  by any court of competent  jurisdiction,
such holding shall not invalidate or render  unenforceable  any other  provision
hereof or any provision of the Indenture.

         Section 8.2 To the extent that any terms of this Supplemental Indenture
or the Notes are inconsistent with the terms of the Indenture, the terms of this
Supplemental Indenture or the Notes shall govern and supersede such inconsistent
terms.

         Section  8.3  This  Supplemental  Indenture  shall be  governed  by and
construed in accordance with the laws of the State of New York.

         Section  8.4 This  Supplemental  Indenture  may be  executed in several
counterparts,  each  of  which  shall  be an  original  and all of  which  shall
constitute but one and the same instrument.

                                      -15-
<PAGE>

         IN WITNESS  WHEREOF,  the  Company  and the  Trustee  have  caused this
Supplemental  Indenture  to be  executed  as an  instrument  under seal in their
respective corporate names as of the date first above written.

                                 SENIOR HOUSING PROPERTIES TRUST

                                 By:___________________________
                                       Name:
                                       Title:

                                 STATE STREET BANK AND TRUST COMPANY, as Trustee

                                 By:___________________________
                                       Name:
                                       Title:

                                      -16-
<PAGE>

                                                                       EXHIBIT A

                                  FORM OF NOTE

                           [Form of Face of Security]

                         SENIOR HOUSING PROPERTIES TRUST

                          8-5/8% Senior Notes due 2012

No. ____                                                           $ ___________

         Senior Housing  Properties  Trust, a real estate  investment trust duly
organized and existing under the laws of Maryland  (herein called the "Company",
which  term  includes  any  successor  Person  under the  Indenture  hereinafter
referred   to),   for   value    received,    hereby    promises   to   pay   to
_____________________________,  or  registered  assigns,  the  principal  sum of
___________________  Dollars  ($_____________)  on January 15, 2012,  and to pay
interest thereon from December 20, 2001 or from the most recent Interest Payment
Date to which  interest has been paid or duly  provided  for,  semi-annually  on
January 15 and July 15 in each  year,  commencing  July 15,  2002 at the rate of
8-5/8% per  annum,  until the  principal  hereof is paid or made  available  for
payment.  The interest so payable,  and punctually paid or duly provided for, on
any Interest  Payment Date will, as provided in such  Indenture,  be paid to the
Person in whose name this Security (or one or more  Predecessor  Securities)  is
registered  at the  close  of  business  on the  Regular  Record  Date  for such
interest,  which  shall be the  January 1 or July 1  (whether  or not a Business
Day), as the case may be, next  preceding  such Interest  Payment Date. Any such
interest not so punctually  paid or duly provided for will forthwith cease to be
payable to the Holder on such Regular  Record Date and may either be paid to the
Person in whose name this Security (or one or more  Predecessor  Securities)  is
registered at the close of business on a Special  Record Date for the payment of
such  Defaulted  Interest to be fixed by the Trustee,  notice  whereof  shall be
given to Holders  of  Securities  of this  series not less than 10 days prior to
such Special  Record Date, or be paid at any time in any other lawful manner not
inconsistent  with the  requirements  of any  securities  exchange  on which the
Securities of this series may be listed, and upon such notice as may be required
by such exchange, all as more fully provided in said Indenture.

         Payment of the principal of (and premium, if any) and any such interest
on this Security will be made at the office or agency of the Company  maintained
for that purpose in such coin or currency of the United  States of America as at
the time of payment is legal  tender for  payment of public and  private  debts;
provided,  however, that at the option of the Company payment of interest may be
made by check  mailed to the  address  of the  Person  entitled  thereto as such
address shall appear in the Security Register.

         Reference is hereby made to the further provisions of this Security set
forth on the reverse  hereof,  which further  provisions  shall for all purposes
have the same effect as if set forth at this place.

         Unless the  certificate of  authentication  hereon has been executed by
the Trustee referred to on the reverse hereof by manual signature, this Security
shall  not be  entitled  to any  benefit  under  the  Indenture  or be  valid or
obligatory for any purpose.

         THE ARTICLES OF AMENDMENT AND RESTATEMENT  ESTABLISHING  SENIOR HOUSING
PROPERTIES  TRUST DATED  SEPTEMBER 20, 1999, A COPY OF WHICH,  TOGETHER WITH ALL
AMENDMENTS  THERETO  (THE  "DECLARATION"),  IS DULY  FILED IN THE  OFFICE OF THE
DEPARTMENT OF ASSESSMENTS  AND TAXATION OF THE STATE OF MARYLAND,  PROVIDES THAT
THE NAME "SENIOR  HOUSING  PROPERTIES  TRUST"  REFERS TO THE TRUSTEES  UNDER THE
DECLARATION  COLLECTIVELY AS TRUSTEES,  BUT NOT INDIVIDUALLY OR PERSONALLY,  AND
THAT NO TRUSTEE, OFFICER, SHAREHOLDER, EMPLOYEE OR AGENT OF THE COMPANY SHALL BE
HELD TO ANY PERSONAL LIABILITY,  JOINTLY OR SEVERALLY, FOR ANY OBLIGATION OF, OR
CLAIM AGAINST,  THE COMPANY.  ALL PERSONS DEALING WITH THE COMPANY,  IN ANY WAY,
SHALL LOOK ONLY TO THE

                                      A-1
<PAGE>

ASSETS OF THE  COMPANY  FOR THE  PAYMENT  OF ANY SUM OR THE  PERFORMANCE  OF ANY
OBLIGATION.

         IN WITNESS  WHEREOF,  the Company has caused this instrument to be duly
executed.

Dated:                                   SENIOR HOUSING PROPERTIES TRUST

                                         By___________________________
                                            Title:

                          CERTIFICATE OF AUTHENTICATION

Dated:

         This is one of the Securities of the series designated therein referred
to in the within-mentioned Indenture.

                                         [STATE STREET BANK AND TRUST COMPANY],
                                         As Trustee

                                         By___________________________
                                            Authorized Officer

                                      A-2
<PAGE>

                          [Form of Reverse of Security]

         1.  General.  This  Security  is  one  of a duly  authorized  issue  of
securities of the Company  (herein  called the  "Securities"),  issued and to be
issued in one or more series under an  Indenture,  dated as of December 20, 2001
(as amended,  supplemented  or otherwise  modified from time to time,  the "Base
Indenture"),  as  supplemented  by a  Supplemental  Indenture No. 1, dated as of
December 20, 2001 (as amended,  supplemented or otherwise  modified from time to
time, the  "Supplemental  Indenture" and the Base Indenture,  as supplemented by
such  Supplemental  Indenture,  the  "Indenture"),  each between the Company and
State Street Bank and Trust  Company,  as Trustee  (herein called the "Trustee",
which term includes any successor trustee under the Indenture), and reference is
hereby  made  to  the  Indenture  for a  statement  of  the  respective  rights,
limitations  of rights,  duties and  immunities  thereunder of the Company,  the
Trustee,  and the  Holders  of the  Securities  and of the terms  upon which the
Securities are, and are to be, authenticated and delivered. This Security is one
of the series designated on the face hereof.

         2. Optional  Redemption.  The  Securities of this series are subject to
redemption  upon not less than 30 nor more than 60 days' notice by mail,  at any
time or from  time to  time,  as a whole  or in  part,  at the  election  of the
Company,  at a redemption  price equal to the sum of (i) the principal amount of
the Notes being redeemed,  (ii) accrued and unpaid interest to but excluding the
applicable Redemption Date and (iii) the Make-Whole Amount, if any.

         In the  event  of  redemption  of this  Security  in part  only,  a new
Security  or  Securities  of this  series and of like  tenor for the  unredeemed
portion  hereof  will be  issued  in the  name of the  Holder  hereof  upon  the
cancellation hereof.

         3. Defeasance.  The Indenture contains provisions for defeasance at any
time of the entire  indebtedness  of this Security upon  compliance with certain
conditions set forth in the Indenture.

         4.  Defaults  and  Remedies.  If an Event of  Default  with  respect to
Securities  of this series shall occur and be  continuing,  the principal of the
Securities of this series may be declared due and payable in the manner and with
the effect provided in the Indenture.

         5. Actions of Holders.  The Indenture permits,  with certain exceptions
as therein  provided,  the amendment  thereof and the modification of the rights
and  obligations  of the Company and the rights of the Holders of the Securities
of each series to be affected under the Indenture at any time by the Company and
the Trustee with the consent of the Holders of a majority in principal amount of
the  Securities  at the time  Outstanding  of each  series to be  affected.  The
Indenture  also  contains   provisions   permitting  the  Holders  of  specified
percentages  in principal  amount of the  Securities  of each series at the time
Outstanding, on behalf of the Holders of all Securities of such series, to waive
compliance  by the Company with certain  provisions of the Indenture and certain
past defaults  under the Indenture and their  consequences.  Any such consent or
waiver by the Holder of this Security  shall be conclusive and binding upon such
Holder and upon all future  Holders of this Security and of any Security  issued
upon the  registration  of transfer  hereof or in  exchange  therefor or in lieu
hereof,  whether  or not  notation  of such  consent or waiver is made upon this
Security.

         As provided  in and subject to the  provisions  of the  Indenture,  the
Holder of this  Security  shall not have the right to institute  any  proceeding
with respect to the Indenture or for the appointment of a receiver or trustee or
for any other remedy thereunder,  unless such Holder shall have previously given
the Trustee written notice of a continuing  Event of Default with respect to the
Securities of this series,  the Holders of not less than a majority in principal
amount of the Securities of this series at the time Outstanding  shall have made
written request to the Trustee to institute proceedings in respect of such Event
of Default as Trustee  and offered the  Trustee  reasonable  indemnity,  and the
Trustee  shall not have  received  from the Holders of a majority  in  principal
amount  of  Securities  of this  series  at the  time  Outstanding  a  direction
inconsistent  with such  request,  and shall have failed to  institute  any such
proceeding,  for 60 days after  receipt  of such  notice,  request  and offer of
indemnity. The foregoing shall not apply to any suit instituted by the Holder of
this  Security for the  enforcement  of any payment of  principal  hereof or any
premium  or  interest  hereon on or after  the  respective  due dates  expressed
herein.

                                      A-3
<PAGE>

         6. Payments Not Impaired.  No reference  herein to the Indenture and no
provision  of this  Security  or of the  Indenture  shall  alter or  impair  the
obligation  of the  Company,  which is absolute  and  unconditional,  to pay the
principal of and any premium and interest on this  Security at the times,  place
and rate, and in the coin or currency, herein prescribed.

         7. Denominations,  Transfer, Exchange. As provided in the Indenture and
subject to certain  limitations therein set forth, the transfer of this Security
is  registrable  in the Security  Register,  upon surrender of this Security for
registration  of  transfer  at the office or agency of the  Company in any place
where the  principal  of and any  premium  and  interest  on this  Security  are
payable, duly endorsed by, or accompanied by a written instrument of transfer in
form  satisfactory  to the Company and the Security  Registrar duly executed by,
the Holder hereof or his attorney duly authorized in writing,  and thereupon one
or  more  new  Securities  of  this  series  and of like  tenor,  of  authorized
denominations and for the same aggregate principal amount, will be issued to the
designated transferee or transferees.

         The  Securities  of this series are issuable  only in  registered  form
without coupons in denominations of $1,000 and any integral multiple thereof. As
provided in the Indenture and subject to certain  limitations therein set forth,
Securities of this series are exchangeable for a like aggregate principal amount
of  Securities  of this  series  and of like  tenor  of a  different  authorized
denomination, as requested by the Holder surrendering the same.

         No service charge shall be made for any such  registration  of transfer
or exchange,  but the Company may require  payment of a sum  sufficient to cover
any tax or other governmental charge payable in connection therewith.

         8. Persons Deemed Owners. Prior to due presentment of this Security for
registration of transfer,  the Company, the Trustee and any agent of the Company
or the Trustee may treat the Person in whose name this Security is registered as
the owner hereof for all purposes,  whether or not this Security be overdue, and
neither the Company,  the Trustee nor any such agent shall be affected by notice
to the contrary.

         9. Defined Terms.  All terms used in this Security which are defined in
the Indenture shall have the meanings assigned to them in the Indenture.

                                      A-4
<PAGE>

                                [ASSIGNMENT FORM]

                                  ABBREVIATIONS

         The following  abbreviations,  when used in the inscription on the face
of this  instrument,  shall be construed as though they were written out in full
according to applicable laws or regulations:

<TABLE>
<S>          <C>                                     <C>                <C>
TEN COM      --  as tenants in common                UNIF GIFT MIN ACT  --   _______ Custodian_______
TEN ENT      --  as tenants by the entireties                                 (Cust)          (Minor)
JT TEN       --  as joint tenants with right of survivorship               Under Uniform Gifts to Minors
                 and not as tenants in common                               Act ___________
                                                                                 (State)
</TABLE>

     Additional abbreviations may also be used though not in the above list.

                     --------------------------------------

FOR VALUE RECEIVED, the undersigned registered holder hereby sell(s),  assign(s)
and transfer(s) unto

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE

  ---------------------------------------------------------------------
 |                                                                     |
 |                                                                     |
  ---------------------------------------------------------------------

________________________________________________________________________________
             PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS OF ASSIGNEE

________________________________________________________________________________
the within security and all rights thereunder,  hereby irrevocably  constituting
and appointing

________________________________________________________________________Attorney
to  transfer  said  security  on the books of the  Company  with  full  power of
substitution in the premises.

Dated:_________________________     Signed:_____________________________________

                                    Notice:  The  signature  to this  assignment
                                    must  correspond with the name as it appears
                                    upon  the  face of the  within  security  in
                                    every  particular,   without  alteration  or
                                    enlargement or any change whatever.

                                    Signature Guarantee*:_______________________

                                    *  Participant  in  a  recognized  Signature
                                    Guarantee   Medallion   Program   (or  other
                                    signature   guarantor   acceptable   to  the
                                    Trustee).

                                      A-5
<PAGE>

                  [FORM OF OPTION OF HOLDER TO ELECT PURCHASE]

                       OPTION OF HOLDER TO ELECT PURCHASE

If you want to elect to have this Note  purchased  by the  Company  pursuant  to
Section 4.2 of the Supplemental  Indenture  referred to in this Note pursuant to
the Company's Change of Control Offer, check this box: [__]

If you want to elect to have  only part of this Note  purchased  by the  Company
pursuant to Section 4.2 of the Supplemental  Indenture  referred to in this Note
pursuant to the Company's Change of Control Offer, state the amount you elect to
have purchased (must be an integral multiple of $1,000): $__________________

PLEASE INSERT YOUR SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER:

  ---------------------------------------------------------------------
 |                                                                     |
 |                                                                     |
  ---------------------------------------------------------------------

Dated:_________________________     Signed:_____________________________________

                                    Notice:  The signature to this election must
                                    correspond  with the name as it appears upon
                                    the  face of the  within  security  in every
                                    particular,     without     alteration    or
                                    enlargement or any change whatever.

                                    Signature Guarantee*:_______________________

                                    *  Participant  in  a  recognized  Signature
                                    Guarantee   Medallion   Program   (or  other
                                    signature   guarantor   acceptable   to  the
                                    Company).

                                      A-6<PAGE>

                                                                     EXHIBIT 4.1

    Number                                                            Shares

                     [NEOGENESIS PHARMACEUTICALS, INC. LOGO]

                        NEOGENESIS PHARMACEUTICALS, INC.

              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE
       THIS CERTIFICATE IS TRANSFERABLE IN BOSTON, MA AND IN NEW YORK, NY

COMMON STOCK                                                        COMMON STOCK
                                                               CUSIP 64049Q 10 1
                                                                 SEE REVERSE FOR
                                                             CERTAIN DEFINITIONS

THIS CERTIFIES THAT

is the owner of

  FULLY PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK, $.001 PAR VALUE, of

NEOGENESIS PHARMACEUTICALS, INC. (the "Corporation") transferable upon the books
of the Corporation by the holder hereof, in person or by duly authorized
attorney, upon the surrender of this Certificate properly endorsed or assigned.
This Certificate and the shares represented hereby are issued and held subject
to the laws of the State of Delaware and to the provisions of the Certificate of
Incorporation and By-Laws of the Corporation, each as now in effect or hereafter
amended. This Certificate is not valid unless and until countersigned by the
Transfer Agent and registered by the Registrar.

IN WITNESS WHEREOF, the Corporation has caused this Certificate to be executed
by the facsimile signatures of its duly authorized officers and sealed with the
facsimile seal of the Corporation.

Dated:

<TABLE>
<S>                                                 <C>                              <C>
[seal of NeoGenesis Pharmaceuticals, Inc.]          /s/ David M. Hunter              /s/ Satish Jindal, Ph.D.
                                                        Chief Financial Officer          President and
                                                        and Treasurer                    Chief Executive Officer
</TABLE>

<PAGE>

                        NEOGENESIS PHARMACEUTICALS, INC.

THE CORPORATION IS AUTHORIZED TO ISSUE MORE THAN ONE CLASS AND SERIES OF STOCK.
THE CORPORATION WILL FURNISH TO THE HOLDER UPON WRITTEN REQUEST AND WITHOUT
CHARGE A STATEMENT OF THE PREFERENCES, VOTING POWERS, QUALIFICATIONS AND SPECIAL
AND RELATIVE RIGHTS OF THE SHARES OF EACH SUCH CLASS AND SERIES.

The following abbreviations, when used in the inscription on the face of this
Certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<TABLE>
<S>                                              <C>
TEN COM -  as tenants in common                  UNIF GIFT MIN ACT -  .............Custodian............
TEN ENT -  as tenants by the entireties                               (cust)                     (Minor)
JT TEN -   as joint tenants with                                      under Uniform Gifts to Minors
           right of survivorship and                                  Act...............................
           not as tenants in common                                                 (State)
COM PROP - as community property
</TABLE>

     Additional abbreviations may also be used though not in the above list.

                                   ASSIGNMENT

For value received,____________________ hereby sells, assigns and transfers unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
    IDENTIFYING NUMBER OF ASSIGNEE

________________________________________________________________________________

________________________________________________________________________________
(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE OF
ASSIGNEE)

________________________________________________________________________________

________________________________________________________________________________

_________________________________________________________________________ shares
of the common stock represented by the within Certificate, and does hereby
irrevocably constitute and appoint

________________________________________________________________________________

________________________________________________________________________________
Attorney to transfer such shares on the books of the within named Corporation
with full power of substitution in the premises.

Dated,
       ------------------------         ----------------------------------------
                                        NOTICE: THE SIGNATURE TO THIS ASSIGNMENT
                                                MUST CORRESPOND WITH THE NAME
                                                AS WRITTEN UPON THE FACE OF THIS
                                                CERTIFICATE IN EVERY PARTICULAR,
                                                WITHOUT ALTERNATION OR
                                                ENLARGEMENT, OR ANY CHANGE
                                                WHATEVER.

                                     -------------------------------------------
SIGNATURE(S) GUARANTEED:             THE SIGNATURE(S) SHOULD BE GUARANTEED BY
                                     AN ELIGIBLE GUARANTOR INSTITUTION (BANKS,
                                     STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS
                                     AND CREDIT UNIONS WITH MEMBERSHIP IN AN
                                     APPROVED SIGNATURE GUARANTEED MEDALLION
                                     PROGRAM), PURSUANT TO S.E.C. RULE 17Ad-15.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00032-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00032-of-00352.parquet"}]]