Airborne particulates were collected over a period of twelve months by the use of Hi-Vol samplers in the basin of Athens, Greece. N-Hexane extracts were tested in a battery of in vitro tests for their ability to induce mutation in bacteria as well as mutation, sister chromatid exchange and morphological transformation in cultured mammalian cells. Positive results were found for mutagenicity with Salmonella strain TA98 in the Ames assay, for sister chromatid exchange induction in CHO cells and for transformation in BALB/c 3T3 cells in culture. They also showed weak non-dose-related induction of ouabain resistance in BALB/c 3T3 cells. The contribution of oxidizing and nitrating agents found in the Athens atmosphere, together with sunlight UV irradiation in the formation of direct acting mutagens and potential carcinogens from ambient polycyclic aromatic hydrocarbons, is suggested.