Aryl hydrocarbon hydroxylase induction was studied in cultured peripheral blood lymphocytes and pulmonary alveolar macrophages from 15 smokers and 8 nonsmokers with a variety of pulmonary diseases. Enzyme levels in lymphocytes from cigarette smokers cultured in medium without an inducing agent were 57±6 mU/106 cells (mean±SEM), while enzyme levels in lymphocytes from nonsmokers were 20±2 mU/106 cells (P < 0.001). When lymphocytes were cultured in the presence of the inducing agent, benzo-(a)anthracene, enzyme activity was increased to 168±23 mU/106 cells in smokers' cells and 99±22 mU/106 cells in lymphocytes from nonsmokers (P < 0.04). When noninduced enzyme values in cultured macrophages were compared, smokers' cells had enzyme levels of 45±5 mU/106 cells, whereas nonsmokers had enzyme activity of 24±2 mU/106 cells (P < 0.002). However, pulmonary macrophages from smokers or nonsmokers, cultured in the presence of benzo(a)-anthracene, had similar levels of induced enzyme activity (P > 0.1). A positive correlation was observed for nonsmokers (r = 0.596, P > 0.1