The rating downgrade on the District of Columbia's series 1991B-2 bonds reflects the substitution of the letter of credit (LOC) provided by National Westminster Bank PLC with a LOC provided by Bank of America. The ratings on the series 1991B-1 and 1991B-3 bonds are affirmed following Standard&Poor's review of the LOCs provided by Société Genérale and Bank of America, respectively. The substitutions of the series 1991B-1 and 1991B-3 LOCs were performed for the purposes of extending the expiration dates. The LOCs for all three series are scheduled to expire on Sept. 26, 2000.