A ryl 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 <0.2) or smokers (r = 0.640, P < 0.04), when enzyme values for noninduced cultures of macrophages and lymphocytes from individual patients were simultaneously compared. Enzyme values for macrophages and lymphocytes cultured in the presence of an inducer also revealed a positive correlation for individual smokers (r = 0.801, P < 0.001) or nonsmokers (r = 0.785, P < 0.01). Inducibility (expressed as fold-induction) for macrophages and lymphocytes from individual patients was also positively correlated (r = 0.889, P < 0.001 for nonsmokers and r = 0.942, P < 0.001 for smokers). These results indicate that the capacity for aryl hydrocarbon hydroxylase induction is similar whether tested in lymphocytes or pulmonary macrophages from this group of pulmonary disease patients.