The mutagenicity of samples of suspended particulates collected from the center of Wroclaw (SW Poland, 642.000 inhabitants) in the period August 1997-July 1998 was studied with the Ames test. The strain Salmonella typhimurium TA 98 and its derivatives with higher nitroreductase (YG 1021) and O-acetyltransferase(YG 1024) activities were used. All samples studied were mutagenic in the Ames test. The mutagenicity of the samples was the highest in winter and the lowest in summer. The air volume corresponding to the dose of particulates required to obtain the mutagenic effect was dependent on the atmospheric concentration of particulates and adsorbed organic compounds. The increase of the mutagenicity of the majority of the samples for the strain TA 98 upon metabolic activation indicates the presence of promutagens in the samples. High activity against the strains YG 1021 and YG 1024 indicates a considerable contribution of nitro and amino derivatives of PAHs to the total mutagenicity of airborne particles. The samples contained PAHs from the EPA list, other Phl-Is and their nitro and amino derivatives, and other aromatics including heterocyclic compounds. (C) 2001 Elsevier Science Ltd. All rights reserved.