EXHIBIT 3.1

                         SENIOR HOUSING PROPERTIES TRUST

                             ARTICLES SUPPLEMENTARY

         Senior  Housing  Properties  Trust,  a Maryland real estate  investment
trust (the "Trust"), hereby certifies to the State Department of Assessments and
Taxation of Maryland, that:

         FIRST:  Under a power  contained in Title 3, Subtitle 8 of the Maryland
General  Corporation  Law (the  "MGCL"),  as  applicable to Maryland real estate
investment trusts, the Trust, by resolution of its Board of Trustees (the "Board
of  Trustees")  duly  adopted at a meeting duly called and held on May 11, 2000,
amended the Bylaws of the Trust (the  "Bylaws") to provide that the Trust elects
to be subject to Section 3-804(b) and (c) of the MGCL.

         SECOND:  The Bylaws described above provide that,  notwithstanding  any
other provision in the  Declaration of Trust or the Bylaws to the contrary,  the
Trust elects to be subject to Section  3-804(b) and (c) of the MGCL,  the repeal
of which may be effected only by a subsequent amendment to the Bylaws adopted or
approved by the Board of Trustees.

         THIRD: These Articles  Supplementary have been approved by the Board of
Trustees in the manner and by the vote required by law.

         FOURTH:  The  undersigned  President  of the Trust  acknowledges  these
Articles  Supplementary  to be the trust act of the Trust and, as to all matters
or  facts  required  to  be  verified  under  oath,  the  undersigned  President
acknowledges that, to the best of his knowledge,  information and belief,  these
matters and facts are true in all material  respects and that this  statement is
made under the penalties of perjury.

         IN WITNESS WHEREOF,  the Trust has caused these Articles  Supplementary
to be  executed  under seal in its name and on its behalf by its  President  and
attested by its Assistant Secretary on this 11th day of May, 2000.

ATTEST:                                SENIOR HOUSING PROPERTIES
                                       TRUST

/s/ Jennifer B. Clark                  /s/ David J. Hegarty   (SEAL)
Jennifer B. Clark,                     David J. Hegarty,
Assistant Secretary                    President