Air pollution, which started to become a serious health concern with industrial revolution, has been threatening human health. Epidemiological studies have reported a close relation between air pollution and respiratory morbidity and mortality. Studies investigating the mechanisms underlying respiratory effects of air pollution have reported that pollutants lead to increased respiratory symptoms, decreased respiratory function and induce inflammatory changes in airways. In vitro studies have demonstrated that air pollutants exert their effects by causing cellular injury directly, and indirectly activating intracellular oxidative pathways. Air way epithelial cells, which form the first line of defence against air pollutants, may play an active role in this pathophysiological course.