Groups of male and female Fischer 344 rats and B6C3F1 mice (80/sex/group) were exposed to vapor concentrations of 0, 150, 500, or 1500 ppm 1,1,1-trichloroethane formulation 6 hr/day, 5 days/week, for 2 years. Ten rats and mice/sex from each group were predesignated for interim sacrifices after 6, 12, and 18 months of exposure. Fifty rats and mice/sex/group were assigned to the study to be terminated after 24 months. Parameters measured during the study included mortality, in-life clinical signs of toxicity, hematology, urinalysis (rats only), clinical chemistry, body weight, organ weights (liver, kidneys, brain, heart, testes), gross pathology, and histopathology. Inhalation exposure of male and female Fischer 344 rats to 1500 ppm vapor of the 1,1,1-trichloroethane formulation for 2 years resulted in a significant decrease in body weights of females. In addition, very slight microscopic hepatic effects were seen in the liver of 1500 ppm-exposed male and female rats necropsied at 6, 12, and 18 months. The hepatic effects could not be discerned at 24 months due to confounding geriatric changes. In the rats exposed to 150 and 500 ppm there were no changes that were considered due to exposure to the 1,1,1-trichloroethane formulation. There were no toxic effects noted in male or female mice at any exposure concentration tested. There were no indications of an oncogenic effect in rats or mice following 2 years of exposure to this 1,1,1-trichloroethane formulation.