AbstractThe genotoxicity of airborne organic particles from forest fire smoke was compared to that from nonsmoky (ambient) urban air using the Salmonella reversion assay and the sister chromatid exchange (SCE) assay in cultured human lymphocytes. Salmonella strains TA98 and TA100 were used with and without the addition of Aroclor‐induced rat liver homogenate (S9). Each sample induced dose‐related increases in mutagenicity and SCE. However, on the basis of the volume of air sampled, the smoke‐filled air induced 12 to 14 times more bacterial reversions in TA100 and 16–38 times more reversions in TA98 than ambient air. Similarly, on a volume basis smoky air induced 43 times more SCE in human lymphocytes than did ambient air. The results indicate that the increased mutagenicity was due not only to the heavier particulate load of the air, but also to the increased specific mutagenicity of the pa