This research was designed to examine the presence of mutagenic/carcinogenic compounds in urban airborne particulate matter in relation to particles aerodynamic size. Inhalable (< 10 microns) airborne particulate (PM-10) was collected at a low traffic site in an industrialized Northern Italian town, using a high volume sampler equipped with a cascade impactor for particles fractionation. The organic extracts of different fractions were examined for mutagenicity in Salmonella typhimurium strains TA98 and TA98/1,8-DNP6 using the microsuspension procedure, and for polycyclic aromatic hydrocarbons (PAHs) content by gas chromatography. Size fractionated particles were also analysed for heavy metals (Fe, Mn, Zn, Pb, Cu, Cd, Cr, Ni, V) using plasma spectrophotometry. The results of mutagenicity and chemical analyses indicate that, at the site investigated, inhalable particulate was largely made of fine (< 0.5 micron) particles, which accounted for most of PAHs and mutagenicity. A similar pattern of distribution was found for heavy metals, which were relatively more abundant in small (< 1.5 microns) particles compared to coarser ones.