The air in Santiago, Chile, is among the most highly polluted in the world. Due to the high levels of pollutants and the high incidence of respiratory diseases, especially in the most susceptible groups, Santiago has been declared a saturated zone for PM(10), O(3), and CO. The aim of this work was to investigate polycyclic aromatic hydrocarbon levels and mutagenic activity of Santiago s fine and coarse fractions of inhalable particles. The levels of 16 polycyclic aromatic hydrocarbons (PAHs) were determined by high-performance liquid chromatography in organic extracts from respirable particles (OERP). Respirable particulate matter (fine and coarse) contains high levels of PAHs including six mutagenic ones classified by the IARC as carcinogenic, which represented at least 45% of the total PAH concentration. A seasonal effect was observed, with higher values in months with lower temperatures. Although a significant decline of PAH levels in OERP was observed in the last years, the levels of carcinogenic PAHs are still higher than those reported in cities of the United States, Australia, and Europe. OERP were highly mutagenic and contained direct and indirect mutagens, which produced both frameshift and base substitution mutations in Salmonella typhimurium. In addition, organic extracts from total suspended particles were also highly mutagenic at the tk locus in h1A1v2 human lymphoblasts in culture. In spite of the important decrease in PAHs in the period 1991-1996, direct mutagenic response has not changed significantly, suggesting that the levels of direct mutagenic pollutants (e.g., nitroarenes) have not decreased considerably during the last years. These results suggest a risk for Santiago s inhabitants since pollutants adsorbed in inhalable particles are highly mutagenic and can damage DNA.