PM10 is the international convention for measuring environmental particulate air pollution. Increases in PM10 have been linked to exacerbations of airways disease and deaths from respiratory and cardiovascular causes. PM10 is a complex and variable mixture but toxicological data suggests that ultrafine particles, transition metals and endotoxins are the most likely components to mediate adverse health effects. Potential mechanisms for the local and systemic adverse effects of PM10 are discussed.