The mutagenicity of airborne particulate matter collected in 17 towns of Italy in 1990 was assessed using the Ames test. The mutagenicity of crude extract correlated with amount of lead, suggesting the direct contribution of gasoline car exhausts. Moreover, the mutagenicity correlated with particulate matter amounts. An inverse correlation with temperature was observed. The crude extracts were fractionated in acid, basic, and neutral fractions. The latter was further separated into polycyclic aromatic hydrocarbon (PAH), polar, and nonpolar fractions. Acid and polar fractions showed the higher mutagenicity. Average recovery of mutagenicity was about 60%.