With a culture technique in gaseous phase which permits a direct contact between cells and the atmosphere, without any liquid interposition, we studied the short-term effects of tobacco smoke on guinea pig alveolar macrophages (AM). Tobacco smoke had a cytotoxic effect on AM as evaluated by the decrease in cell ATP content, total smoke appearing more toxic than the gas phase. Toxicity of smoke gas phase is also ascertained by morphologic cell changes in electron microscopy and by a decrease in cell bactericidal activity. The large variation in AM susceptibility is not related to cell content in superoxide dismutase but seems to be in good correlation with AM glutathione content, especially when cells are cultured with N-acetylcysteine. However, the protective glutathione action is not total and seems less important than the one observed with a low concentration of NO2 (0.2 ppm/24 hours).