Exhibit 3.4

                                  AMENDMENT TO
                   CERTIFICATE OF DETERMINATION OF PREFERENCES
                                       OF
                      8-7/8% SERIES X CUMULATIVE REDEEMABLE
                                 PREFERRED STOCK
                                       OF
                             PS BUSINESS PARKS, INC.

            [As filed in the office of the Secretary of State of the
                   State of California on September 24, 1999]


        The undersigned, David Goldberg and Jack E. Corrigan, Vice President and
Secretary,  respectively,  of PS BUSINESS PARKS, INC., a California  corporation
(the "Corporation"), do hereby certify:

        FIRST:  Pursuant to and in accordance with the provisions of Section 401
of the California  Corporations  Code and the Restated Articles of Incorporation
of the  Corporation,  the Board of Directors of the Corporation has duly adopted
the resolution attached hereto as Exhibit A and incorporated herein by reference
authorizing and increasing the authorized  number of shares of the Corporation's
8-7/8%  Series  X  Cumulative  Redeemable  Preferred  Stock  from  1,200,000  to
1,600,000, for a net increase of 400,000 shares.

        SECOND:  None  of  the  shares  of the  Corporation's  8-7/8%  Series  X
Cumulative Redeemable Preferred Stock has been issued.

        We further  declare under penalty of perjury under the laws of the State
of California  that the matters set forth in the foregoing  certificate are true
and correct of our own knowledge.

        IN WITNESS WHEREOF,  the undersigned have executed this certificate this
23rd day of September, 1999.


                                        /s/ DAVID GOLDBERG
                                        --------------------------
                                        David Goldberg, Vice President


                                        /s/ JACK E. CORRIGAN
                                        --------------------------
                                        Jack E. Corrigan, Secretary




                                    EXHIBIT A

                      RESOLUTION OF THE BOARD OF DIRECTORS
                           OF PS BUSINESS PARKS, INC.

                       INCREASING THE AUTHORIZED NUMBER OF
                            SHARES OF 8-7/8% SERIES X
                      CUMULATIVE REDEEMABLE PREFERRED STOCK


        RESOLVED:  That  pursuant to the authority  conferred  upon the Board of
Directors  by Article  III of the  Restated  Articles of  Incorporation  of this
Corporation  and the  resolutions  creating the  corporation's  8-7/8%  Series X
Cumulative  Redeemable  Preferred Stock,  the number of shares  constituting the
corporation's 8-7/8% Series X Cumulative Redeemable Preferred Stock is increased
from 1,200,000 shares to 1,600,000 shares.