Chronic toxicity and oncogenicity were evaluated in groups of male and female Fischer 344 rats (80/sex/group) exposed to chlorothene (1,1,1-trichloroethane) by inhalation at 0, 150, 500, or 1500 ppm for 6 hrs/day, 5 days/week for 2 years. The body weights of female animals were significantly decreased compared to controls at various times throughout the study, whereas relative and absolute organ weights were unaffected. The hematology, urinalysis, and clinical chemistry values were unaffected by the treatments. Necropsy of animals sacrificed at 6, 12 and 18 months of exposure revealed no significant exposure-related effects and there were no significant differences in the incidence of tumor-like lesions in the control or exposed rats. Microscopic examination of the livers of animals exposed to 1500 ppm revealed an exposure-related accentuation of the normal hepatic lobular pattern consisting of altered cytoplasmic staining in the cells surrounding the central vein. Chronic toxicity and oncogenicity were also evaluated in groups of 80 male and 80 female B6C3F1 miceexposed to chlorothene in the same manner as above. The body weights of both males and females in all exposure groups were comparable to the controls. All other findings correlated to those described above for rats.