Rats, guinea pigs, dogs, rabbits, and monkeys were exposed to trichloroethylene, carbon tetrachloride, 1,1,1-trichloroethane, dichlorodifluoromethane, and 1,1-dichloroethylene. Two types of inhalation experiments were conducted: continuous exposure for 90 days and 8-hour exposures, 5 days a week, for a total of thirty exposures. The parameters studied included mortality, visible signs of toxicity, and hematologic, biochemical, pathologic, and body weight changes. Throughout this entire study which encompassed 17 separate exposures over a period of nearly four years, no visible signs of toxicity were noted in any species exposed to these materials. Significant mortality was found in both the repeated (515 mg/m 3) and continuous (61 mg/m 3) exposures to carbon tetrachloride as well as in the continuous exposures to 1,1-dichloroethylene at 189, 101, and 61 mg/m 3. Growth depression in varying degrees was found in all continuous exposures involving trichloroethylene, carbon tetrachloride, and 1,1-dichloroethylene and in the repeated exposures to carbon tetrachloride. No significant hematologic alterations were noted in any of the studies. No biochemical studies were done in the earlier years and hence no biochemical data were obtained from the animals exposed to trichloroethylene and dichlorodifluoromethane. Serum urea nitrogen levels were within control limits in all of the exposures to carbon tetrachloride, 1,1-dichloroethylene, and 1,1,1-trichloroethane in which determinations were made. Liver lipid contents in guinea pigs were found to be significantly elevated following repeated exposure to 515 mg/m 3 of carbon tetrachloride. Significant elevations of serum glutamic-pyruvic transaminase and liver alkaline phosphatase activities were found in rats and guinea pigs following continuous exposure to 189 mg/m 3 of 1,1-dichloroethylene. Histopathologic study revealed liver damage following continuous exposures to high levels of dichlorodifluoromethane (3997 mg/m 3), and to lower levels of carbon tetrachloride (61 mg/m 3), and 1,1-dichloroethylene (189 mg/m 3). Similar liver damage was also found in the repeated exposures to the two latter materials at 515 mg/m 3 and 395 mg/m 3, respectively.