This U.S. Bureau of Mines study examines the effect of a ceramic particle trap and a manganese fuel additive on the mutagenic activity and chemical composition of diesel exhaust particulate matter from a heavy-duty mining engine. Particles were collected by dilution tunnel sampling from a four-cylinder, caterpillar 3304, naturally aspirated, indirect-injection engine operated at six steady-state conditions. Depending on engine load and speed, the ceramic particle trap reduced the following emissions: particulate matter, 80 to 94 pct; soluble organic fraction (sof), 83 to 95 pct; 1-nitropyrene, 94 to 96 pct; and sof mutagenicity, 72 pct (cycle- weighted average). When the manganese fuel additive was used without a ceramic particle trap, the total cycle mutagenic activity emitted increased sevenfold, in part due to elevated emissions of 1- nitropyrene. When used with the trap at the recommended concentration, the manganese additive lowers the trap regeneration temperature by 65 deg c, sof removal efficiency from 86 to 62 pct, and removal efficiency for mutagenic substances from 72 to 43 pct.