EXHBIIT 4.19


                                    FORM OF

                               GUARANTEE AGREEMENT

                                     between

                         SENIOR HOUSING PROPERTIES TRUST

                                       and

                       STREET STATE BANK AND TRUST COMPANY


                     Relating to the Preferred Securities of
                               SNH CAPITAL TRUST I


                            Dated as of June 21, 2001

<PAGE>

    Certain Sections of this Agreement relating to Sections 310 through 318,
                 inclusive, of the Trust Indenture Act of 1939:

Trust Indenture
  Act Section                                                  Agreement Section

ss.310(a)(1)................................................................4.1
      (a)(2)................................................................4.1
      (a)(3).....................................................Not Applicable
      (a)(4).....................................................Not Applicable
      (a)(5)................................................................4.1
      (b)..............................................................2.8, 4.1
      (c)........................................................Not Applicable
ss.311(a)...................................................................2.2
      (b)...................................................................2.2
      (c)........................................................Not Applicable
ss.312......................................................................2.2
ss.313......................................................................2.3
ss.314(a)...................................................................2.4
      (b)........................................................Not Applicable
      (c)...................................................................2.5
      (d)........................................................Not Applicable
      (e)...................................................................1.1
ss.315(a)..............................................................3.1, 3.2
      (b)...................................................................2.7
      (c)...................................................................3.1
      (d)...................................................................3.2
ss.316(a)(1)(A).............................................................5.4
      (a)(1)(B).............................................................2.6
      (a)(2).....................................................Not Applicable
      (b)...................................................................5.4
      (c)........................................................Not Applicable
ss.317......................................................................2.1
ss.318......................................................................2.1



----------------------
         NOTE: This reconciliation and tie shall not, for any purpose, be deemed
to be part of the Agreement.

<PAGE>

                               GUARANTEE AGREEMENT


This GUARANTEE  AGREEMENT,  dated as of June 21, 2001, is executed and delivered
by SENIOR HOUSING PROPERTIES TRUST, a Maryland real estate investment trust (the
"Guarantor")  and STATE STREET BANK AND TRUST  COMPANY,  a  Massachusetts  trust
company,  as trustee (the "Guarantee  Trustee"),  for the benefit of the Holders
(as defined  herein) from time to time of the Preferred  Securities  (as defined
herein)  of SNH  Capital  Trust I, a  Maryland  statutory  business  trust  (the
"Issuer").

         WHEREAS,  pursuant  to an Amended and  Restated  Trust  Agreement  (the
"Trust Agreement"), dated as of June 21, 2001, among the Trustees named therein,
the  Guarantor,  as  Depositor,  and the Holders  from time to time of undivided
beneficial  interests  in the assets of the Issuer,  the Issuer is issuing up to
$28,750,000 of its 10.125% Trust Preferred Securities (liquidation amount $25.00
per preferred  security) (the  "Preferred  Securities")  representing  preferred
undivided  beneficial interests in the assets of the Issuer and having the terms
set forth in the Trust Agreement;

         WHEREAS,  the Preferred Securities will be issued by the Issuer and the
proceeds  thereof,  together with the proceeds from the issuance of the Issuer's
Common  Securities  (as  defined  below),  will  be used to  purchase  the  Debt
Securities  (as defined in the Trust  Agreement) of the Guarantor  which will be
deposited  with State Street Bank and Trust Company,  as Property  Trustee under
the Trust Agreement, as trust assets; and

         WHEREAS, as incentive for the Holders to purchase Preferred Securities,
the Guarantor desires  irrevocably and  unconditionally  to agree, to the extent
set  forth  herein,  to pay to the  Holders  of  the  Preferred  Securities  the
Guarantee Payments (as defined herein) and to make certain other payments on the
terms and conditions set forth herein;

         NOW,  THEREFORE,  in  consideration  of the  purchase by each Holder of
Preferred  Securities,  which purchase the Guarantor hereby agrees shall benefit
the Guarantor,  the Guarantor executes and delivers this Guarantee Agreement for
the benefit of the Holders from time to time of the Preferred Securities.

                                   ARTICLE I

                                   DEFINITIONS

         SECTION 1.1 Definitions. As used in this Guarantee Agreement, the terms
set forth below shall, unless the context otherwise requires, have the following
meanings.  Capitalized or otherwise defined terms used but not otherwise defined
herein shall have the meanings  assigned to such terms in the Trust Agreement as
in effect on the date hereof.

         "Additional Sums" means such additional  amounts as may be necessary in
order  that the  amount of  distributions  due and  payable by the Issuer on the
Preferred  Securities and Common Securities that at any time remain  outstanding
in  accordance  with the terms  thereof  shall not be reduced as a result of any
additional taxes, duties, assessments and other governmental charges of whatever
nature,  imposed by the United States  government or any other taxing  authority
(but
<PAGE>

not including  withholding taxes imposed on holders of such Preferred Securities
and Common Securities).

         "Affiliate" of any specified  Person means any other Person directly or
indirectly controlling or controlled by or under direct common control with such
specified Person;  provided,  however,  that an Affiliate of the Guarantor shall
not be deemed to  include  the  Issuer.  For the  purposes  of this  definition,
"control"  when used with  respect to any  specified  Person  means the power to
direct the  management  and  policies of such  Person,  directly or  indirectly,
whether  through the ownership of voting  securities,  by contract or otherwise;
and the terms  "controlling" and "controlled"  have meanings  correlative to the
foregoing.

         "Common Securities" means the securities representing common beneficial
interests in the assets of the Issuer.

         "Debentures" means up to $29,639,200 of the 10.125% Junior Subordinated
Debentures  due  June  15,  2041  of  the  Guarantor  issuable  pursuant  to the
Indenture.

         "Event of  Default"  means a  default  by the  Guarantor  on any of its
payment or other obligations under this Guarantee Agreement;  provided, however,
that, except with respect to a default in payment of any Guarantee Payments,  no
Event of Default shall be deemed to have occurred under this Guarantee Agreement
unless and until the  Guarantor  shall have received  written  notice of default
from the Guarantee  Trustee and shall not have cured such default within 60 days
after receipt of such notice.

         "Guarantee  Payments"  means the following  payments or  distributions,
without duplication, with respect to the Preferred Securities, to the extent not
paid or made by or on behalf  of the  Issuer:  (i) any  accumulated  and  unpaid
Distributions  (as  defined in the Trust  Agreement)  required to be paid on the
Preferred Securities,  to the extent the Issuer shall have funds on hand legally
available  therefor  at such time,  (ii) the  redemption  price set forth in the
Trust Agreement, including premium, if any, all accrued and unpaid Distributions
to the  date  of  redemption  (the  "Redemption  Price"),  with  respect  to the
Preferred  Securities  called  for  redemption  by the  Issuer to the extent the
Issuer shall have funds on hand  legally  available  therefor,  and (iii) upon a
voluntary or involuntary  dissolution,  winding-up or liquidation of the Issuer,
other than in connection with the distribution of Debt Securities to the Holders
or the redemption of all Preferred  Securities issued by the Issuer,  the lesser
of (a) the aggregate of the liquidation  amount of $25.00 per Preferred Security
plus accrued and unpaid Distributions on the Preferred Securities to the date of
payment to the extent the Issuer shall have funds on hand  legally  available to
make such payment and (b) the amount of assets of the Issuer remaining available
for  distribution  to Holders in  liquidation of the Issuer (in either case, the
"Liquidation Distribution").

         "Guarantee Trustee" means State Street Bank and Trust Company,  until a
Successor Guarantee Trustee has been appointed and has accepted such appointment
pursuant to the terms of this Guarantee Agreement and thereafter means each such
Successor Guarantee Trustee.

         "Holder"  means any holder,  as  registered on the books and records of
the Issuer, of any Preferred Securities;  provided, however, that in determining
whether the holders of the  requisite

                                      -2-
<PAGE>

percentage of Preferred  Securities have given any request,  notice,  consent or
waiver  hereunder,  "Holder"  shall not include  the  Guarantor,  the  Guarantee
Trustee or any Affiliate of the Guarantor or the Guarantee Trustee.

         "Indenture"  means the Junior  Subordinated  Indenture dated as of June
21, 2001 with respect to the Debt  Securities,  between the  Guarantor and State
Street Bank and Trust Company,  as trustee,  as the same may be supplemented and
amended from time to time.

         "List of Holders" has the meaning specified in Section 2.2(a).

         "Majority in Liquidation  Amount of the  Securities"  means,  except as
provided by the Trust Indenture Act, a vote by the Holder(s),  voting separately
as a class,  of more  than 50% of the  aggregate  liquidation  amount of all the
outstanding Preferred Securities issued by the Issuer.

         "Officers'   Certificate"   means,   with  respect  to  any  Person,  a
certificate  signed by (i) the  Chairman  of the Board,  a Vice  Chairman of the
Board, the Chief Executive Officer,  the Chief Operating Officer,  the President
or a Vice President,  and (ii) the Chief Financial  Officer,  the Treasurer,  an
Assistant Treasurer, the Controller,  the Secretary or an Assistant Secretary of
such Person,  delivered to the  Guarantee  Trustee.  Any  Officer's  Certificate
delivered with respect to compliance  with a condition or covenant  provided for
in this Guarantee Agreement shall include:

         (a) a statement that each officer signing the Officers' Certificate has
read the covenant or condition and the definitions relating thereto;

         (b) a brief  statement  of the nature and scope of the  examination  or
investigation undertaken by each officer in rendering the Officers' Certificate;

         (c) a statement  that each such  officer has made such  examination  or
investigation as, in such officer's opinion, is necessary to enable such officer
to express an informed  opinion as to whether or not such  covenant or condition
has been complied with; and

         (d) a  statement  as to whether,  in the opinion of each such  officer,
such condition or covenant has been complied with.

         "Person" means a legal person,  including any individual,  corporation,
estate, partnership,  joint venture,  association,  joint stock company, limited
liability  company,  trust,  unincorporated  association,  or  government or any
agency or political subdivision thereof, or any other entity of whatever nature.

         "Property  Trustee" means State Street Bank and Trust Company,  serving
as property trustee under the Indenture.

         "Responsible Officer", when used with respect to the Guarantee Trustee,
means the chairman or any vice-chairman of the board of directors,  the chairman
or any vice-chairman of the executive  committee of the board of directors,  the
chairman  of the  trust  committee,  the  president,  any  vice  president,  the
secretary,  any assistant secretary, the treasurer, any assistant treasurer, the
cashier,  any assistant  cashier,  any trust officer or assistant trust officer,
the controller or any assistant controller or any other officer of the Guarantee
Trustee  customarily

                                      -3-
<PAGE>

performing  functions  similar to those performed by any of the above designated
officers and also means,  with respect to a particular  corporate  trust matter,
any other  officer to whom such matter is referred  because of his  knowledge of
and familiarity with the particular subject.

         "Senior  Indebtedness of the Guarantor"  means (i) any  indebtedness of
the  Guarantor  for borrowed or  purchased  money,  whether or not  evidenced by
bonds, debentures,  notes or other written instruments,  (ii) obligations of the
Guarantor  for  reimbursement  under  letters of credit,  banker's  acceptances,
security purchase facilities or similar facilities issued for the account of the
Guarantor,  (iii) any  indebtedness  or other  obligations of the Guarantor with
respect to commodity  contracts  (including  but not limited to contracts in the
spot,  forward and markets,  options,  and contracts for differences),  interest
rate commodity and currency swap agreements,  cap, floor and collar  agreements,
currency  spot  and  forward   contracts,   and  other  similar   agreements  or
arrangements  designed to protect  against  fluctuations  in  commodity  prices,
currency  exchange  or interest  rates,  and (iv) any  guarantees,  endorsements
(other than by  endorsement  of  negotiable  instruments  for  collection in the
ordinary course of business) or other similar contingent  obligations in respect
of  obligations  of  others of a type  described  in (i),  (ii) or (iii)  above,
whether or not such  obligation  is classified as a liability on a balance sheet
prepared in accordance with generally accepted  accounting  principles,  in each
case listed in (i), (ii),  (iii) and (iv) above whether  outstanding on the date
of execution of this Indenture or thereafter  incurred,  other than  obligations
ranking  on a parity  with the  Guarantee  Payments  or  ranking  junior  to the
Guarantee  Payments;   provided,  however,  that  "Senior  Indebtedness  of  the
Guarantor" does not include obligations to trade creditors.

         "Subsidiary"  means any  corporation (or the equivalent type of entity)
more than 50% of the outstanding  voting securities of which is owned,  directly
or indirectly, by the Guarantor or by one or more other Subsidiaries,  or by the
Guarantor  and  one or  more  other  Subsidiaries.  For  the  purposes  of  this
definition,  "voting  securities"  means securities which ordinarily have voting
power for the election of directors or trustees, whether at all times or only so
long as no senior  class of  securities  has such voting  power by reason of any
contingency.

         "Successor  Guarantee  Trustee"  means a  successor  Guarantee  Trustee
possessing the qualifications to act as Guarantee Trustee under Section 4.1.

         "Trust  Indenture  Act"  means  the  Trust  Indenture  Act of 1939,  as
amended.

                                   ARTICLE II

                               TRUST INDENTURE ACT

         SECTION  2.1  Trust  Indenture  Act;  Application.  (a) This  Guarantee
Agreement  is  subject to the  provisions  of the Trust  Indenture  Act that are
required  to be  part of this  Guarantee  Agreement  and  shall,  to the  extent
applicable, be governed by such provisions.

         (b) If and to the extent that any provision of this Guarantee Agreement
limits,  qualifies or conflicts  with the duties imposed by Sections 310 to 317,
inclusive, of the Trust Indenture Act, such imposed duties shall control.

                                      -4-
<PAGE>

         SECTION 2.2 List of Holders.  (a) The Guarantor  shall furnish or cause
to be furnished to the Guarantee Trustee (unless the Guarantee Trustee is acting
as Security  Registrar with respect to the Debt Securities  under the Indenture)
(i)  semi-annually,  not later than January 15 and July 15 in each year, a list,
in such form as the Guarantee  Trustee may  reasonably  require of the names and
addresses of the Holders ("List of Holders") as of the preceding  December 31 or
June 30,  as the case may be,  and  (ii) at such  other  times as the  Guarantee
Trustee  may  request  in  writing,  within  30 days  after the  receipt  by the
Guarantor of any such  request,  a List of Holders as of a date not more than 15
days prior to the time such list is  furnished,  in each case to the extent such
information  is in  the  possession  or  control  of  the  Guarantor  and is not
identical to a previously  supplied  list of Holders or has not  otherwise  been
received by the Guarantee Trustee.  Notwithstanding the foregoing, the Guarantor
shall not be obligated to provide such List of Holders at any time the Preferred
Securities are  represented by one or more Global  Securities (as defined in the
Indenture).  The  Guarantee  Trustee may destroy any List of Holders  previously
given to it on receipt of a new List of Holders.

         (b) The  Guarantee  Trustee  shall  comply with its  obligations  under
Section 311(a), Section 311(b) and Section 312(b) of the Trust Indenture Act.

         SECTION 2.3 Reports by the Guarantee Trustee.  Within 60 days of May 15
of each calendar year,  the Guarantee  Trustee shall provide to the Holders such
reports as are  required by Section 313 of the Trust  Indenture  Act, if any, in
the form and in the manner  provided by Section 313 of the Trust  Indenture Act.
The Guarantee  Trustee shall also comply with the requirements of Section 313(d)
of the Trust Indenture Act.

         SECTION 2.4 Periodic Reports to Guarantee Trustee.  The Guarantor shall
provide to the Guarantee Trustee, the Securities and Exchange Commission and the
Holders such documents,  reports and information, if any, as required by Section
314 of the  Trust  Indenture  Act and the  compliance  certificate  required  by
Section  314 of the Trust  Indenture  Act in the form,  in the manner and at the
times required by Section 314 of the Trust Indenture Act.

         SECTION 2.5  Evidence of  Compliance  with  Conditions  Precedent.  The
Guarantor  shall  provide to the  Guarantee  Trustee such evidence of compliance
with such conditions precedent, if any, provided for in this Guarantee Agreement
that  relate  to any of the  matters  set forth in  Section  314(c) of the Trust
Indenture  Act. Any  certificate  or opinion  required to be given by an officer
pursuant  to  Section  314(c)(1)  may be  given  in  the  form  of an  Officers'
Certificate.

         SECTION  2.6 Events of  Default;  Waiver.  The Holders of a Majority in
Liquidation  Amount of the  Securities  may, by vote,  on behalf of the Holders,
waive any past  default  or Event of  Default  and its  consequences.  Upon such
waiver,  any such  default or Event of  Default  shall  cease to exist,  and any
default  or Event of  Default  arising  therefrom  shall be  deemed to have been
cured, for every purpose of this Guarantee  Agreement,  but no such waiver shall
extend to any  subsequent  or other  default  or Event of  Default or impair any
right consequent therefrom.

         SECTION 2.7 Event of Default;  Notice. (a) The Guarantee Trustee shall,
within 90 days after the  occurrence  of an Event of Default,  transmit by mail,
first class postage  prepaid,  to the Holders,  notices of all Events of Default
known to the Guarantee Trustee,  unless such defaults have been cured before the
giving of such notice;  provided,  that,  except in the case of a

                                      -5-
<PAGE>

default in the payment of a Guarantee  Payment,  the Guarantee  Trustee shall be
protected in  withholding  such notice if and so long as the Board of Directors,
the executive  committee or a trust  committee of directors  and/or  Responsible
Officers of the Guarantee  Trustee in good faith determines that the withholding
of such notice is in the interests of the Holders.

         (b) The Guarantee  Trustee shall not be deemed to have knowledge of any
Event of Default  unless the  Guarantee  Trustee  shall  have  received  written
notice,  or a Responsible  Officer charged with the  administration of the Trust
Agreement shall have obtained written notice, of such Event of Default.

         SECTION  2.8  Conflicting  Interests.   The  Trust  Agreement  and  the
Indenture  shall  be  deemed  to be  specifically  described  in this  Guarantee
Agreement  for the  purposes  of clause (i) of the first  proviso  contained  in
Section 310(b) of the Trust Indenture Act.

                                  ARTICLE III

               POWERS, DUTIES AND RIGHTS OF THE GUARANTEE TRUSTEE

         SECTION  3.1  Powers  and  Duties of the  Guarantee  Trustee.  (a) This
Guarantee  Agreement  shall be held by the Guarantee  Trustee for the benefit of
the  Holders,  and the  Guarantee  Trustee  shall not  transfer  this  Guarantee
Agreement to any Person except a Holder exercising his or her rights pursuant to
Section  5.4(iv)  or to a  Successor  Guarantee  Trustee on  acceptance  by such
Successor  Guarantee  Trustee of its  appointment to act as Successor  Guarantee
Trustee.   The  right,  title  and  interest  of  the  Guarantee  Trustee  shall
automatically vest in any Successor  Guarantee Trustee,  upon acceptance by such
Successor Guarantee Trustee of its appointment  hereunder,  and such vesting and
cessation of title shall be effective whether or not conveyancing documents have
been  executed  and  delivered  pursuant to the  appointment  of such  Successor
Guarantee Trustee.

         (b) If an Event of Default actually known to the Responsible Officer of
the Guarantee  Trustee has occurred and is  continuing,  the  Guarantee  Trustee
shall enforce this Guarantee Agreement for the benefit of the Holders.

         (c) The  Guarantee  Trustee,  before  the  occurrence  of any  Event of
Default  and after the curing of all Events of Default  that may have  occurred,
shall  undertake  to perform only such duties as are  specifically  set forth in
this  Guarantee  Agreement,  and no  implied  covenants  shall be read into this
Guarantee  Agreement against the Guarantee Trustee.  In case an Event of Default
has occurred (that has not been cured or waived  pursuant to Section 2.6) and is
actually  known  to the  Responsible  Officer  of  the  Guarantee  Trustee,  the
Guarantee  Trustee shall  exercise such of the rights and powers vested in it by
this  Guarantee  Agreement,  and use the same  degree  of care and  skill in its
exercise  thereof,  as  a  prudent  person  would  exercise  or  use  under  the
circumstances in the conduct of his or her own affairs.

         (d) No  provision  of this  Guarantee  Agreement  shall be construed to
relieve the Guarantee Trustee from liability for its own negligent  action,  its
own negligent failure to act or its own willful misconduct, except that:

                                      -6-
<PAGE>

                  (i) prior to the  occurrence of any Event of Default and after
         the  curing or  waiving  of all such  Events of  Default  that may have
         occurred;

                           (A)  the  duties  and  obligations  of the  Guarantee
                  Trustee shall be determined  solely by the express  provisions
                  of this Guarantee  Agreement,  and the Guarantee Trustee shall
                  not be liable  except for the  performance  of such duties and
                  obligations  as are  specifically  set forth in this Guarantee
                  Agreement; and

                           (B) in the  absence  of bad  faith on the part of the
                  Guarantee  Trustee,  the  Guarantee  Trustee may  conclusively
                  rely, as to the truth of the statements and the correctness of
                  the  opinions  expressed  therein,  upon any  certificates  or
                  opinions  furnished to the Guarantee Trustee and conforming to
                  the requirements of this Guarantee Agreement;  but in the case
                  of any such  certificates  or opinions  that by any  provision
                  hereof or of the Trust Indenture Act are specifically required
                  to be  furnished  to  the  Guarantee  Trustee,  the  Guarantee
                  Trustee shall be under a duty to examine the same to determine
                  whether  or not  they  conform  to the  requirements  of  this
                  Guarantee Agreement;

                  (ii) the  Guarantee  Trustee shall not be liable for any error
         of  judgment  made  in  good  faith  by a  Responsible  Officer  of the
         Guarantee Trustee, unless it shall be proved that the Guarantee Trustee
         was  negligent  in  ascertaining  the  pertinent  facts upon which such
         judgment was made;

                  (iii) the  Guarantee  Trustee shall not be liable with respect
         to any  action  taken or  omitted  to be  taken by it in good  faith in
         accordance  with  the  direction  of the  Holders  of not  less  than a
         Majority in Liquidation Amount of the Securities  relating to the time,
         method and place of conducting any proceeding for any remedy  available
         to the Guarantee  Trustee,  or exercising any trust or power  conferred
         upon the Guarantee Trustee under this Guarantee Agreement; and

                  (iv) no provision of this  Guarantee  Agreement  shall require
         the  Guarantee  Trustee  to expend  or risk its own funds or  otherwise
         incur  personal  financial  liability in the  performance of any of its
         duties  or in the  exercise  of any of its  rights  or  powers,  if the
         Guarantee Trustee shall have reasonable  grounds for believing that the
         repayment of such funds or liability  is not  reasonably  assured to it
         under the  terms of this  Guarantee  Agreement  or  adequate  indemnity
         against such risk or liability is not reasonably assured to it.

         SECTION 3.2 Certain  Rights of  Guarantee  Trustee.  (a) Subject to the
provisions of Section 3.1:

                  (i)  The  Guarantee  Trustee  may  rely  and  shall  be  fully
         protected  in acting or  refraining  from acting  upon any  resolution,
         certificate,  statement,  proxy,  instrument,  opinion, report, notice,
         request,  direction,  consent,  order,  bond,  debenture,  note,  other
         evidence of indebtedness  or other paper or document  believed by it to
         be genuine and to have been  signed,  sent or  presented  by the proper
         party or parties.

                                      -7-
<PAGE>

                  (ii) Any  direction or act of the  Guarantor  contemplated  by
         this  Guarantee  Agreement  shall  be  sufficiently   evidenced  by  an
         Officers' Certificate unless otherwise prescribed herein.

                  (iii)  Whenever,  in  the  administration  of  this  Guarantee
         Agreement,  the Guarantee Trustee shall deem it desirable that a matter
         be proved or established  before taking,  suffering or omitting to take
         any action  hereunder,  the Guarantee Trustee (unless other evidence is
         herein specifically prescribed) may, in the absence of bad faith on its
         part,  request  and rely  upon an  Officers'  Certificate  which,  upon
         receipt of such request from the Guarantee  Trustee,  shall be promptly
         delivered by the Guarantor.

                  (iv) The Guarantee Trustee may consult with legal counsel, and
         the written  advice or opinion of such legal  counsel  with  respect to
         legal matters shall be full and complete  authorization  and protection
         in respect of any action  taken,  suffered or omitted to be taken by it
         hereunder in good faith and in accordance  with such advice or opinion.
         Such legal  counsel may be legal counsel to the Guarantor or any of its
         Affiliates and may be one of its employees. The Guarantee Trustee shall
         have  the  right  at any  time  to  seek  instructions  concerning  the
         administration of this Guarantee  Agreement from any court of competent
         jurisdiction.

                  (v) The  Guarantee  Trustee  shall be under no  obligation  to
         exercise  any of the  rights or powers  vested in it by this  Guarantee
         Agreement at the request or direction of any Holder, unless such Holder
         shall have provided to the Guarantee Trustee such adequate security and
         indemnity as would  satisfy a reasonable  person in the position of the
         Guarantee Trustee,  against the costs,  expenses (including  attorneys'
         fees and  expenses)  and  liabilities  that might be  incurred by it in
         complying  with such request or direction,  including  such  reasonable
         advances as may be requested by the  Guarantee  Trustee;  provided that
         nothing  contained in this Section  3.2(a)(v) shall be taken to relieve
         the Guarantee Trustee,  upon the occurrence of an Event of Default,  of
         its  obligation  to exercise the rights and powers vested in it by this
         Guarantee  Agreement  and use the same  degree of care and skill in the
         exercise  thereof as a prudent  person would  exercise or use under the
         circumstances in the conduct of his or her own affairs.

                  (vi)  The  Guarantee  Trustee  shall  not be bound to make any
         investigation  into the  facts or  matters  stated  in any  resolution,
         certificate,  statement,  instrument, opinion, report, notice, request,
         direction,  consent,  order, bond,  debenture,  note, other evidence of
         indebtedness or other paper or document,  but the Guarantee Trustee, in
         its  discretion,  may make such further inquiry or  investigation  into
         such facts or matters as it may see fit.

                  (vii) The  Guarantee  Trustee may execute any of the trusts or
         powers  hereunder or perform any duties hereunder either directly or by
         or through its agents or attorneys or any Affiliate,  and the Guarantee
         Trustee shall not be

                                      -8-
<PAGE>

         responsible  for any  misconduct  or negligence on the part of any such
         agent or attorney appointed with due care by it hereunder.

                  (viii)  Whenever  in  the  administration  of  this  Guarantee
         Agreement  the  Guarantee  Trustee  shall deem it  desirable to receive
         instructions  with respect to  enforcing  any remedy or right or taking
         any other  action  hereunder,  the  Guarantee  Trustee  (A) may request
         instructions  from the Holders of a Majority in  Liquidation  Amount of
         the Securities,  (B) may refrain from enforcing such remedy or right or
         taking such other action until such instructions are received,  and (C)
         shall be protected in acting in accordance with such instructions.

                  (ix) Any action taken by the  Guarantee  Trustee or its agents
         hereunder  shall bind the Holders,  and the  signature of the Guarantee
         Trustee  or its agents  alone  shall be  sufficient  and  effective  to
         perform any such action. No third party shall be required to inquire as
         to  the  authority  of  the  Guarantee  Trustee  to so act or as to its
         compliance  with any of the  terms  and  provisions  of this  Guarantee
         Agreement  both  of  which  shall  be  conclusively  evidenced  by  the
         Guarantee Trustee's or its agent's taking such action.

         (b) No provision of this Guarantee  Agreement shall be deemed to impose
any duty or obligation  on the  Guarantee  Trustee to perform any act or acts or
exercise any right, power, duty or obligation  conferred or imposed on it in any
jurisdiction  in which it shall be illegal,  or in which the  Guarantee  Trustee
shall be  unqualified  or  incompetent  in accordance  with  applicable  law, to
perform  any such act or acts or to  exercise  any such  right,  power,  duty or
obligation.  No permissive power or authority available to the Guarantee Trustee
shall  be  construed  to be a duty to act in  accordance  with  such  power  and
authority.

         SECTION 3.3 Indemnity.  The Guarantor agrees to indemnify the Guarantee
Trustee for,  and to hold it harmless  against,  any loss,  liability or expense
incurred without  negligence or bad faith on the part of the Guarantee  Trustee,
arising out of or in connection  with the acceptance or  administration  of this
Guarantee  Agreement,  including the reasonable  costs and expenses of defending
itself  against  any claim or  liability  in  connection  with the  exercise  or
performance of any of its powers or duties hereunder. The Guarantee Trustee will
not claim or exact any lien or charge on any  Guarantee  Payment  as a result of
any amount due to it under this Guarantee Agreement.

                                   ARTICLE IV

                                GUARANTEE TRUSTEE

         SECTION  4.1  Guarantee  Trustee;  Eligibility.  (a) There shall at all
times be a Guarantee Trustee which shall:

                  (i) not be an Affiliate of the Guarantor; and

                  (ii)  be a  Person  that is  eligible  pursuant  to the  Trust
         Indenture Act to act as such and has a combined  capital and surplus of
         at  least  $50,000,000,   and

                                      -9-
<PAGE>

         shall be a corporation  meeting the  requirements  of Section 310(a) of
         the Trust  Indenture  Act.  If such  corporation  publishes  reports of
         condition at least annually,  pursuant to law or to the requirements of
         the supervising or examining authority,  then, for the purposes of this
         Section and to the extent  permitted  by the Trust  Indenture  Act, the
         combined capital and surplus of such corporation  shall be deemed to be
         its combined capital and surplus as set forth in its most recent report
         of condition so published.

         (b) If at any time the Guarantee  Trustee shall cease to be eligible to
so act under Section 4.1(a),  the Guarantee Trustee shall immediately  resign in
the manner and with the effect set out in Section 4.2(c).

         (c) If the  Guarantee  Trustee has or shall  acquire  any  "conflicting
interest"  within the meaning of Section 310(b) of the Trust  Indenture Act, the
Guarantee Trustee and Guarantor shall in all respects comply with the provisions
of  Section  310(b) of the Trust  Indenture  Act.  The Trust  Agreement  and the
Indenture  shall  not be  deemed  to  constitute  conflicting  interests  of the
Guarantee Trustee.

         SECTION 4.2  Appointment,  Removal  and  Resignation  of the  Guarantee
Trustee. (a) Subject to Section 4.2(b) the Guarantee Trustee may be appointed or
removed without cause at any time by the Guarantor.

         (b) The  Guarantee  Trustee  shall not be  removed in  accordance  with
Section  4.2(a) until a Successor  Guarantee  Trustee has been appointed and has
accepted  such  appointment  by written  instrument  executed by such  Successor
Guarantee Trustee and delivered to the Guarantor.

         (c) The  Guarantee  Trustee  appointed to office  hereunder  shall hold
office until a Successor  Guarantee  Trustee shall have been  appointed or until
its  removal or  resignation.  The  Guarantee  Trustee  may resign  from  office
(without  need for prior or subsequent  accounting)  by an instrument in writing
executed  by  the  Guarantee  Trustee  and  delivered  to the  Guarantor,  which
resignation  shall not take effect until a Successor  Guarantee Trustee has been
appointed and has accepted such appointment by an instrument in writing executed
by such  Successor  Guarantee  Trustee and  delivered to the  Guarantor  and the
resigning Guarantee Trustee.

         (d) If no Successor  Guarantee  Trustee  shall have been  appointed and
accepted  appointment  as  provided  in this  Section  4.2  within 60 days after
delivery  to the  Guarantor  of an  instrument  of  resignation,  the  resigning
Guarantee  Trustee may petition,  at the expense of the Guarantor,  any court of
competent  jurisdiction for appointment of a Successor  Guarantee Trustee.  Such
court may  thereupon,  after  prescribing  such  notice,  if any, as it may deem
proper, appoint a Successor Guarantee Trustee.

                                      -10-
<PAGE>

                                   ARTICLE V

                                    GUARANTEE

         SECTION 5.1 Guarantee.  The Guarantor  irrevocably and  unconditionally
agrees,  subject to Section 5.8 and Article 8, to pay in full to the Holders the
Guarantee  Payments  (without  duplication of amounts  theretofore paid by or on
behalf of the Issuer),  as and when due,  regardless  of any  defense,  right of
set-off or  counter  claim  which the  Issuer may have or assert  other than the
defense of payment.  The Guarantor's  obligation to make a Guarantee Payment may
be satisfied by direct  payment of the required  amounts by the Guarantor to the
Holders  or by  causing  the  Issuer to pay such  amounts  to the  Holders.  The
Guarantor's  obligations  to make  Guarantee  Payments are not guaranteed by the
Guarantor's Subsidiaries.

         SECTION 5.2 Waiver of Notice and Demand.  The  Guarantor  hereby waives
notice of acceptance of the Guarantee Agreement and of any liability to which it
applies or may apply,  presentment,  demand for payment,  any right to require a
proceeding  first  against the  Guarantee  Trustee,  Issuer or any other  Person
before proceeding against the Guarantor,  protest, notice of nonpayment,  notice
of dishonor, notice of redemption and all other notices and demands.

         SECTION 5.3  Obligations  Not  Affected.  The  obligations,  covenants,
agreements and duties of the Guarantor  under this Guarantee  Agreement shall in
no way be affected or impaired by reason of the  happening  from time to time of
any of the following:

         (a) the release or waiver,  by  operation of law or  otherwise,  of the
performance  or  observance  by the Issuer of any express or implied  agreement,
covenant, term or condition relating to the Preferred Securities to be performed
or observed by the Issuer;

         (b) the  extension  of time for the payment by the Issuer of all or any
portion of the Distributions,  Redemption Price, Liquidation Distribution or any
other sums payable under the terms of the Preferred  Securities or the extension
of time for the performance of any other obligation under, arising out of, or in
connection with, the Preferred  Securities  (other than an extension of time for
payment of Distributions that results from the extension of any interest payment
period on the Debt Securities as so provided in the Indenture);

         (c) any  failure,  omission,  delay or lack of diligence on the part of
the Holders to enforce, assert or exercise any right, privilege, power or remedy
conferred on the Holders pursuant to the terms of the Preferred  Securities,  or
any action on the part of the Issuer  granting  indulgence  or  extension of any
kind;

         (d) the voluntary or involuntary liquidation,  dissolution, sale of any
collateral, receivership,  insolvency, bankruptcy, assignment for the benefit of
creditors, reorganization,  arrangement, composition or readjustment of debt of,
or other similar proceedings  affecting,  the Issuer or any of the assets of the
Issuer;

         (e) any  invalidity  of, or  defect or  deficiency  in,  the  Preferred
Securities;

         (f) the settlement or compromise of any obligation guaranteed hereby or
hereby incurred; or

                                      -11-
<PAGE>

         (g) any other circumstance whatsoever that might otherwise constitute a
legal or equitable  discharge or defense of a guarantor,  it being the intent of
this  Section  5.3 that the  obligations  of the  Guarantor  hereunder  shall be
absolute and unconditional under any and all circumstances.

         There shall be no obligation of the Holders or the Guarantee Trustee to
give  notice to, or obtain the  consent of, the  Guarantor  with  respect to the
happening of any of the foregoing.

         SECTION 5.4 Rights of Holders.  The  Guarantor  expressly  acknowledges
that: (i) this Guarantee  Agreement will be deposited with the Guarantee Trustee
to be held for the benefit of the Holders;  (ii) the  Guarantee  Trustee has the
right to enforce this  Guarantee  Agreement on behalf of the Holders;  (iii) the
Holders of a Majority in Liquidation  Amount of the Securities have the right to
direct the time,  method and place of conducting  any  proceeding for any remedy
available to the Guarantee Trustee in respect of this Guarantee  Agreement or to
direct the exercise of any trust or power  conferred upon the Guarantee  Trustee
under this Guarantee Agreement; (iv) any Holder may institute a legal proceeding
directly  against  the  Guarantor  to enforce  its rights  under this  Guarantee
Agreement,  without first  instituting a legal proceeding  against the Guarantee
Trustee,  the Issuer or any other  Person;  and (v) if an Event of Default  with
respect to the Debt  Securities  constituting  the  failure to pay  interest  or
principal  on the Debt  Securities  on the date such  interest or  principal  is
otherwise payable has occurred and is continuing, then any Holder shall have the
right,  which is absolute and  unconditional,  to proceed  directly  against the
Guarantor to obtain Guarantee Payments without first waiting to determine if the
Guarantee  Trustee has enforced this Guarantee  Agreement or instituting a legal
proceeding against the Issuer, the Guarantee Trustee or any other Person.

         SECTION 5.5 Guarantee of Payment.  This Guarantee  Agreement  creates a
guarantee of payment and not of collection. This Guarantee Agreement will not be
discharged  except  by  payment  of the  Guarantee  Payments  in  full  (without
duplication of amounts  theretofore paid by the Issuer) or upon  distribution of
Debt Securities to Holders as provided in the Trust Agreement.

         SECTION 5.6  Subrogation.  The Guarantor shall be subrogated to all (if
any) rights of the Holders  against the Issuer in respect of any amounts paid to
the Holders by the Guarantor  under this Guarantee  Agreement and shall have the
right to waive payment by the Issuer pursuant to Section 5.1; provided, however,
that the  Guarantor  shall not  (except  to the  extent  required  by  mandatory
provisions  of law) be entitled to enforce or exercise  any rights  which it may
acquire  by  way  of  subrogation  or  any  indemnity,  reimbursement  or  other
agreement,  in all cases as a result of payment under this Guarantee  Agreement,
if, at the time of any such  payment,  any amounts are due and unpaid under this
Guarantee  Agreement.  If any amount shall be paid to the Guarantor in violation
of the preceding sentence, the Guarantor agrees to hold such amount in trust for
the Holders and to pay over such amount to the Guarantor Trustee for the benefit
of the Holders.

         SECTION 5.7 Independent  Obligations.  The Guarantor  acknowledges that
its obligations  hereunder are independent of the obligations of the Issuer with
respect to the Preferred  Securities  and that the Guarantor  shall be liable as
principal and debtor hereunder to make Guarantee  Payments pursuant to the terms
of this Guarantee Agreement notwithstanding

                                      -12-
<PAGE>

the  occurrence  of any  event  referred  to in  subsections  (a)  through  (g),
inclusive, of Section 5.3 hereof.

         SECTION 5.8 Subordination.  The Guarantee  Agreement will constitute an
unsecured  obligation  of the Guarantor and will rank junior in right of payment
to the Senior  Indebtedness  of the Guarantor in the same manner and to the same
extent  as set  forth in  Article  Fourteen  of the  Indenture.  Each  Holder of
Preferred  Securities,  by its acceptance  thereof,  agrees to the subordination
provisions and other terms of this Guarantee Agreement.

         If an "Event of Default" (as defined in the Indenture) has occurred and
is continuing,  the rights of holders of Common  Securities to receive Guarantee
Payments under the Common Securities  Guarantee Agreement are subordinate to the
rights of the Holders of  Preferred  Securities  to receive  Guarantee  Payments
under this Guarantee Agreement.

                                   ARTICLE VI

                                    COVENANTS

         (a) Certain Covenants of the Guarantor. (a) The Guarantor covenants and
agrees (i) to  maintain  directly or  indirectly  100%  ownership  of the Common
Securities;  provided that any successors or assigns of the Guarantor  permitted
by  the  Indenture  may  succeed  to the  Guarantor's  ownership  of the  Common
Securities,  (ii) not to voluntarily terminate,  wind-up or liquidate the Issuer
except (A) in connection with a distribution of the Debentures to the holders of
the Preferred  Securities in liquidation of the Issuer or (B) in connection with
any merger,  consolidation  or amalgamation  permitted by the Trust Agreement of
the Issuer, and (iii) to use its reasonable  efforts,  consistent with the terms
and  provisions  of the Trust  Agreement  of the Issuer,  to cause the Issuer to
remain  classified  as a grantor  trust for  United  States  Federal  income tax
purposes.

         (b) The  Guarantor  covenants and agrees that if and so long as (i) the
Property Trustee is the Holder of all the Debentures on behalf of the Issuer and
(ii) the  Guarantor  has  elected,  and has not revoked  such  election,  to pay
Additional  Sums, the Guarantor  shall pay to the Issuer the Additional  Sums in
respect of the Preferred Securities and Common Securities.

                                  ARTICLE VII

                                   TERMINATION

         SECTION 7.1 Termination. This Guarantee Agreement shall terminate as to
each Holder with respect to the Preferred  Securities of the Issuer and be of no
further force and effect upon the earliest of (i) full payment of the redemption
price of all Preferred  Securities,  (ii) distribution of the Debt Securities of
the  Guarantor  held by the Issuer to the  Holders or (iii) full  payment of the
amounts payable in accordance  with the Trust Agreement upon  liquidation of the
Issuer. Notwithstanding the foregoing, this Guarantee Agreement will continue to
be  effective  or will be  reinstated,  as the case  may be,  if at any time any
Holder must restore payment of any

                                      -13-
<PAGE>

sums paid under such Preferred Securities or this Guarantee Agreement.


                                  ARTICLE VIII

                                  MISCELLANEOUS

         SECTION 8.1  Successors  and Assigns.  All  guarantees  and  agreements
contained  in this  Guarantee  Agreement  shall  bind the  successors,  assigns,
receivers,  trustees and representatives of the Guarantor and shall inure to the
benefit of the Holders of the Preferred  Securities then outstanding.  Except in
connection with a consolidation,  merger or sale involving the Guarantor that is
permitted  under  Article 8 of the  Indenture and pursuant to which the assignee
agrees  in  writing  to  perform  the  Guarantor's  obligations  hereunder,  the
Guarantor shall not assign its obligations hereunder.

         SECTION 8.2 Amendments. Except with respect to any changes which do not
adversely  affect the rights of the  Holders in any  material  respect (in which
case no consent of the Holders will be required),  this Guarantee  Agreement may
only be  amended  with the  prior  approval  of the  Holders  of not less than a
Majority in Liquidation Amount of the Securities. The provisions of Article 6 of
the Trust Agreement concerning meetings of the Holders shall apply to the giving
of such  approval.  The Guarantor  shall  furnish the Guarantee  Trustee with an
Officers' Certificate and an Opinion of Counsel to the effect that any amendment
of this Agreement is authorized and permitted and that all conditions precedent,
if any, in this  Guarantee  Agreement,  to the  execution  and  delivery of such
amendment have been satisfied.

         SECTION  8.3  Notices.  Any  notice,  request  or  other  communication
required or permitted to be given hereunder shall be in writing,  duly signed by
the party giving such notice, and delivered, telecopied or mailed by first class
mail as follows:

         (a) if given to the  Guarantor,  to the address set forth below or such
other address as the Guarantor may give notice of to the Holders:

                  Senior Housing Properties Trust
                  400 Centre Street
                  Newton, Massachusetts 02458
                  Attention:  Treasurer

         (b) if given to the Issuer,  in care of the Guarantee  Trustee,  at the
Issuer's  (and the  Guarantee  Trustee's)  address set forth below or such other
address as the  Guarantee  Trustee on behalf of the Issuer may give notice of to
the Holders:


                  SNH Capital Trust I
                  c/o Senior Housing Properties Trust
                  400 Centre Street
                  Newton, Massachusetts 02458
                  Attention:  Treasurer

                                      -14-
<PAGE>

with a copy to:

                  State Street Bank and Trust Company
                  2 Avenue de Lafayette
                  Boston, Massachusetts 02111
                  Attention:  Paul D. Allen, Corporate Trust Department

         (c) if given to any  Holder,  at the address set forth on the books and
records of the Issuer.

         All notices  hereunder shall be deemed to have been given when received
in person,  telecopied  with receipt  confirmed,  or mailed by first class mail,
postage  prepaid,  except that if a notice or other document is refused delivery
or cannot be  delivered  because  of a changed  address  of which no notice  was
given,  such notice or other  document shall be deemed to have been delivered on
the date of such refusal or inability to deliver.

         SECTION 8.4 Benefit. This Guarantee Agreement is solely for the benefit
of the Holders and is not separately transferable from the Preferred Securities.

         SECTION 8.5  Interpretation.  In this Guarantee  Agreement,  unless the
context otherwise requires:

         (a) capitalized terms used in this Guarantee  Agreement but not defined
in the preamble hereto have the
respective meanings assigned to them in Section 1.1;

         (b) a term defined  anywhere in this  Guarantee  Agreement has the same
meaning throughout;

         (c) all  references to "the  Guarantee  Agreement"  or "this  Guarantee
Agreement" are to this Guarantee Agreement as modified,  supplemented or amended
from time to time;

         (d) all references in this Guarantee Agreement to Articles and Sections
are to  Articles  and  Sections of this  Guarantee  Agreement  unless  otherwise
specified;

         (e) a term defined in the Trust Indenture Act has the same meaning when
used in this  Guarantee  Agreement  unless  otherwise  defined in this Guarantee
Agreement or unless the context otherwise requires;

         (f) a reference to the singular includes the plural and vice versa; and

         (g) the masculine, feminine or neuter genders used herein shall include
the masculine, feminine and neuter genders.

         SECTION 8.6 Governing Law. THIS GUARANTEE  AGREEMENT  SHALL BE GOVERNED
BY AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW
YORK WITHOUT REGARD TO THE CONFLICTS OF LAW PRINCIPLES THEREOF.

                                      -15-
<PAGE>

         This instrument may be executed in any number of counterparts,  each of
which so executed shall be deemed to be an original,  but all such  counterparts
shall together constitute but one and the same instrument.

         THIS GUARANTEE AGREEMENT is executed as of the day and year first above
written.

                               SENIOR HOUSING PROPERTIES TRUST


                               By:
                                  --------------------------------------------
                                      Name: David J. Hegarty
                                      Title: President


                               STATE STREET BANK AND TRUST COMPANY


                               -----------------------------------,
                               as Guarantee Trustee


                               By:
                                  --------------------------------------------
                                      Name:
                                      Title:


                                      -16-