Model systems for the study of carcinogenesis in cultured human bronchus, peripheral lung, and pulmonary alveolar macrophages have been developed. Explants of human bronchus and peripheral lung have been maintained in culture for 4 months and 24 days, respectively. The metabolism of several classes of chemical carcinogens has been investigated in human bronchus, and that of benzo(a)pyrene in peripheral lung and alveolar macrophages. Human bronchial epithelial cells have been grown and maintained in culture for periods of 3-4 months. Attempts are being made to improve the culture conditions for these cells. It is anticipated that these model systems will be useful for: 1) identification of environmental carcinogens for human lung; 2) determination of the metabolic pathways for carcinogens in these tissues; 3) identifying host factors determining susceptibility to chemically induced lung cancer; and 4) evaluating new methods of prophylactic intervention in populations at high risk of developing lung cancer.