In experimental exposure studies with ozone or nitrogen dioxide a change in lung function and unspecific airway sensitivity was observed. These effects were paralleled by an induction of cellular and biochemical changes. The exposure of isolated cells in vitro led to a decrease in vitality, an increase in permeability and the secretion of mediators very similar to the composition found in bronchoalveolar lavage after in vivo exposure. The cell culture model, therefore, allows the study of the mechanism of these oxidative air pollutants and allows further the understanding of the influence of different cell types on the observed effects in vivo.