Diesel particulate emissions were collected from five 1979 through 1983 light-duty vehicles. All vehicles were fueled with a No. 2 reference fuel; and one vehicle was also fueled with 25% blends of SRC-II, SRC-II plus cetane improver and high aromatic fuel mixed with the reference fuel, and a reference fuel resulting in 10 fuel-vehicle combinations. The later reference fuel-vehicle test was designed to be a repeat emission test of an earlier test to demonstrate the repeatability of the particulate collection and sample processing of duplicate vehicle samples.The particulate-laden filters were extracted with methylene chloride, and selected filters were subsequently extracted with an azeotropic mixture of toluene: ethanol. The extracts were chromatographically separated into three fractions, and one fraction was subdivided into six additional fractions. All fractions were Ames-tested using TA-98 without addition of S-9. Selected fractions were analyzed for pyrene and benzo (a) pyrene and nitropyrene.The results of this study show that the mutagenic activity was primarily concentrated in a fraction containing nitro-PAH compounds. The mutagenic activity for this fraction accounted for 42 to 90% of the total sample activity, yet the weight-percent of this fraction ranged from 6 to 13% of the total extract mass. The remaining mutagenic activity was found in three other fractions containing polar compounds.The mutagenic activity in the particulate extracts from a vehicle fueled with the SRC-II and high aromatic fuel blends was 30 to 50% higher than particulate extracts using the reference fuel. Also, the mutagenic activity was significantly lower in the extracts using the jet fuel.