Exhibit 12(b)
                                  CERTIFICATION

     Mark D. Nerud,  President and Principal  Executive  Officer,  and Daniel W.
Koors,  Treasurer and Principal  Financial  Officer of Montgomery  Street Income
Securities, Inc. (the "Fund"), each certify that to his knowledge:

     1. This Form N-CSR filing for the Fund fully complies with the requirements
of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

     2. The  information  contained in this Form N-CSR fairly  presents,  in all
material  respects,  the  financial  condition  and results of operations of the
Fund.



/s/ Mark D. Nerud                           /s/ Daniel W. Koors
By: Mark D. Nerud                           By: Daniel W. Koors
President and                               Treasurer and
Principal Executive Officer                 Principal Financial Officer

Date: September 8, 2006                     Date: September 8, 2006