Mobile and stationary sources emit particle-bound organics that have demonstrated mutagenicity. The objective of this study was to measure the mutagenicity of the fractionated organic emissions from diesel, cigarette smoke condensate (CSC), coke oven and roofing tar in the Ames assay. This study demonstrated significant biological differences among the four emission sources. Within each source, the relative mutagenicity of each fraction was significantly different in the presence and absence of an exogenous metabolic activation. In the diesel sample, over 90% of the mutagenic activity is located in the aromatic and polar neutral (PN) fractions, and a significant portion of this activity can be accounted for by nitro-PNAs. Most of the mutagenicity of the coke oven main sample was found in the BASE and PN fractions which contained aromatic amines and nitrogen heterocycles. The CSC sample also had a high percent of the mutagenic activity in the BASE fraction. Chemical analysis however, indicates that the components in the CSC differed significantly from those of the coke oven main sample. The roofing tar sample contained aromatic and polar mutagenic constituents that were not NO2-PNAs. Although the specific mutagens in these different sources are not identical, they all cause frameshift mutations and appear to be compounds that could be classified as polycyclic organic matter (POM).