Mutagenic activity of extractable organic matter (EOM), from airborne particles collected over winters in four towns of Czech Republic, was investigated by the means of Salmonella typhimurium indicator strains TA98 and YG1041 using the Ames plate incorporation assay. Mutagenicity of all tested samples showed significant dose-related increase in number of revertants per mg of EOM. The direct mutagenic potency detected with TA98 increased further in the presence of external metabolic activation. The mutagenic potency detected with YG1041 was about two orders of magnitude higher than that detected with TA98. The mutagenicity results correlated with the concentrations of the polycyclic aromatic hydrocarbons (PAHs) determined by GC/MS. Local differences in mutagenicity, expressed as numbers of revertants per m3 of air, were observed with the highest values in Prague air samples. For routine ambient air mutagenicity monitoring, the use of YG1041 and the plate incorporation test are recommendable.