Document:

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                                                                     Exhibit 4.6

                  [Letterhead of The Meditrust Companies]

                                                     April 30, 1998

The Holders who are parties to
that certain Registration Rights Agreement
dated January 3, 1998
c/o William P. Hallman
Suite 3200
Texas Commerce Bank Tower
201 Main Street
Fort Worth, TX 76102

         RE:      REGISTRATION RIGHTS AGREEMENT DATED JANUARY 3, 1998

Dear Mr. Hallman:

         Reference is made to that certain Registration Rights Agreement dated
January 3, 1998 (the "Registration Rights Agreement") by and between Meditrust
Corporation (the "Company"), Meditrust Operating Company ("OPCO") and each of
the signatories thereto (collectively, the "Holders"). All capitalized terms
used in this letter without definition shall have the meanings ascribed to them
in the Registration Rights Agreement.

         In consideration of the Holders entering into Amendment No. 1 dated of
even date herewith to the Shareholders Agreement dated January 3, 1998 by and
among the Company, OPCO and the Holders, and other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, the
Company and OPCO agree that the third sentence of Section 2(a) of the
Registration Rights Agreement shall be amended to read as follows:

         "The Company and OPCO agree to use reasonable efforts to keep the Shelf
         Registration Statement (or any amendment thereto or replacement or
         successor thereto) continuously effective until the earlier of (a) five
         (5) years from the Effective Date or the date on which the applicable
         Holders (or Distributee or other Holder Transferees) no longer hold any
         Registrable Securities.

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Mr. William P. Hallman
April 30, 1998
Page 2

         The Company and OPCO also further acknowledge that the remaining terms
and conditions of the Registration Rights Agreement not specifically addressed
by this letter agreement remain in full force and effect.

                                                 Very truly yours,

                                                 /S/DAVID F. BENSON
                                                 ---------------------------
                                                 David F. Benson
                                                   President
                                                   Meditrust Corporation

                                                 /S/MICHAEL J. BOHNEN
                                                 ---------------------------
                                                 Michael J. Bohnen
                                                   Secretary
                                                   Meditrust Operating Company<PAGE>

                                                                     Exhibit 4.7

                                                September 15, 1999

Meditrust Corporation                            Meditrust Operating Company
197 First Avenue                                 197 First Avenue
Suite 300                                        Suite 100
Needham, MA 02194                                Needham, MA 02194

Ladies and Gentlemen:

         We refer to that certain Registration Rights Agreement dated as of
January 3, 1998 by and among the undersigned and you, as amended and extended
(as so amended and extended, the "Registration Rights Agreement"). Each of the
undersigned hereby agrees that the time periods for filing the Shelf
Registration Statement (as defined in the Registration Rights Agreement) and
causing such Shelf Registration Statement to be declared effective by the
Securities and Exchange Commission are hereby reinstated and extended to
February 1, 2000 and March 1, 2000, respectively. Except for the foregoing
extensions, all other terms of the Registration Rights Agreement remain in full
force and effect.

                                                THOMAS M. TAYLOR & CO.

                                                By: /S/W.P. HALLMAN, JR.
                                                    ----------------------------
                                                    Name:  W.P. Hallman, Jr.
                                                    Title:    Vice President

                                                SID R. BASS, INC.

                                                By: /S/W.P. HALLMAN, JR.
                                                    ----------------------------
                                                    Name:  W.P. Hallman, Jr.
                                                    Title:    Vice President

                                                                  EXECUTION COPY

<PAGE>

                                        LEE M. BASS, INC.

                                        By: /S/W.P. HALLMAN, JR.
                                            ------------------------------------
                                            Name:  W.P. Hallman, Jr.
                                            Title:    Vice President

                                        THE BASS MANAGEMENT TRUST

                                        By: /S/W.P. HALLMAN
                                            ------------------------------------
                                            Perry R. Bass, Trustee,
                                            by W.P. Hallman, Attorney-in-fact

                                        THE AIRLIE GROUP, L.P.

                                        By:  EBD, L.P., General Partner,
                                            ------------------------------------
                                             By:  TMT-FW Inc.,

                                                       By: /S/W.P. HALLMAN, JR.
                                                           ---------------------
                                                              W.P. Hallman, Jr.
                                                              Vice President

                                        /S/WILLIAM P. HALLMAN, JR.
                                        ----------------------------------------
                                        WILLIAM P. HALLMAN, JR.

                                        ANNIE R. BASS GRANDSON'S TRUST FOR
                                        LEE M. BASS

                                        By: /S/WILLIAM P. HALLMAN, JR.
                                        ----------------------------------------
                                            William P. Hallman, Jr., Trustee

                                                                  EXECUTION COPY

                                        2

<PAGE>

                                     ANNIE R. BASS GRANDSON'S TRUST FOR
                                     SID R. BASS

                                     By: /S/WILLIAM P. HALLMAN, JR.
                                         ---------------------------------------
                                         William P. Hallman, Jr., Trustee

                                     /S/PETER STERLING
                                     -------------------------------------------
                                     PETER STERLING

                                     /S/ GARY L. MEAD
                                     -------------------------------------------
                                     GARY L. MEAD

                                     HYATT ANNE BASS SUCCESSOR TRUST

                                     By:  Panther City Investment Co., Trustee

                                            By: /S/W.P. HALLMAN, JR.
                                                --------------------------------
                                                W.P. Hallman Jr.,
                                                Vice President

                                     SAMANTHA SIMS BASS SUCCESSOR TRUST

                                     By:  Panther City Investment Co., Trustee

                                            By: /S/W. P. HALLMAN, JR.
                                                --------------------------------
                                                W.P. Hallman Jr.,
                                                Vice President

                                                                  EXECUTION COPY

                                        3

<PAGE>

                                      PORTFOLIO C INVESTORS, L.P.

                                      By:  Portfolio Associates, Inc.,
                                             General Partner

                                             By: /S/W.P. HALLMAN, JR.
                                                 -------------------------------
                                                 W.P. Hallman Jr.,
                                                 Vice President

Accepted and agreed to as of this 15th day of September, 1999.

                                      MEDITRUST CORPORATION

                                      By: /S/MICHAEL S. BENJAMIN
                                          --------------------------------------
                                          Name: Michael S. Benjamin, Esq.
                                          Title:   Senior Vice President

                                      MEDITRUST OPERATING COMPANY

                                      By: /S/MICHAEL S. BENJAMIN
                                          --------------------------------------
                                          Name: Michael S. Benjamin, Esq.
                                          Title: Authorized Agent

                                                                  EXECUTION COPY

                                        4

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