The paper gives results of tests (to aid in developing emission rules) in July and August 1991 on a 360-tonne/day mass burn municipal waste combustor (MWC) at the Ogden Martin Systems of Stanislaus, Inc. facility near Crows Landing, CA. Test results indicated that carbon (C) addition was effective in improving mercury (Hg) removal: removal increased with increasing C feed rate. Hg removal improved from about 30% without C addition to over 90% at the highest C feed rate tested. The test data obtained for evaluation of the secondary test objectives suggested that (1) ammonia (NH3) addition (which occurred with low slip) had no apparent adverse effect on Hg control, (2) lime stoichiometry had no effect on Hg emissions over the narrow range studied, (3) the fabric filter (FF) gas temperature over the range tested did not affect Hg control, and (4) the Hg content of ash/residue stream samples remained relatively constant over a period of 28 days in samples held at 54 C.