The aim of this work was to evaluate the mutagenic activity of airborne particulate matter in the rubber industry. Air was sucked through Whatman glass-fibre filters with Staplex pumps and adsorbed substances and fume particles were extracted with acetone or toluene for 2 h in a ultrasonic cleaner. After separation of the insoluble solid phase by filtration, solvent was evaporated at a temperature of 70°C in an argon atmosphere. The residue was stored at -20°C. Mutagenicity was determined by the Salmonella plate incorporation assay with the tester strain TA98 and activity is related either to the weight of aerosol (rev mg-I) or to the volume of atmospheric sample (rev m-3). The fumes emitted from the tyre tread line, calender feeding, and tyre vulcanizing processes, showed the highest mutagenic activity (55-211 rev mg-', + S9). At these and at other workplaces (extruder mill, carbon black station, mixer loading), mutagenic activity related to the volume of air was in the range of 22-158 rev w3, + S9. The results indicate the need to reduce and monitor mutagenic contamination in order to increase the safety of work in the rubber industry.