Male strain A/J mice were exposed for 5 mo in a whole-body inhalation chamber to 3 different concentrations of a mixture of cigarette sidestream and mainstream smoke (99, 120, and 176 mg/m(3) of total suspended particulate material, TSP). After an additional 4-mo recovery period in air, lung tumor multiplicities and incidences were determined. The two highest smoke concentrations produced significantly more lung tumors than did the low dose and control groups, although the response to the high was slightly less than to the medium dose. Lung tumor incidences were in all three groups significantly higher than in controls. Lung displacement volume was increased in a dose-dependent manner, but morphometric analysis of the tissues failed to provide evidence for airspace enlargement. Plasma cotinine levels were dose-dependent and similar after 1-day and 5-day exposure. The shape of the dose-response curve and a comparison with previous data suggest that cigarette smoke is only a comparatively weak mouse lung carcinogen.