The ability of particulate pollutants to act on the mitotic cell division process and to induce aneuploidy in V79 cell cultures has been investigated. Extracts of airborne particulates and particulate car exhaust caused mitotic arrest connected with a dose-dependent increase in the incidence of initial and full C-metaphases. Furthermore, numerical chromosome alterations such as hyperdiploidy and polyploidy in subsequent cell divisions were induced with increasing concentrations. These findings indicate that particulate pollutants from the ambient air and from car exhaust contain potent spindle poisons with the ability to produce mitotic aneuploidy in mammalian cells. The significance of these results is that induced aneuploidy by particulate pollutants represents a genetic and somatic risk to exposed populations.