Although there are many possible approaches to the study of chemical-induced lung injury, it has become clear in recent years that it is important, particularly for mechanistic studies, to clarify the responses of specific target cells in the lungs. The alveolar macrophage has been extensively studied because of its important role in the response of the lung to inhaled dusts and in the development of inflammatory lung disorders, and because it is a cell type that can be easily obtained from animals and humans by the technique of bronchoalveolar lavage. The type II cell and the Clara cell have important physiological functions and they are considered to be the main sites for the biotransformation of xenobiotics in the lung. In recent years methods have been developed to isolate, purify and culture these cells from laboratory animals. The greatest promise of these in vitro techniques is in the possibility of studying human cells, and thus coming closer to scientifically sound extrapolations of experimental data to the human situation.