Long-term trials were carried out with rats fed mash fumigated with carbon tetrachloride or ethylene dichloride (1,2-dichloroethane). The difficulty of maintaining a constant residual level of fumigant in the feed was overcome by adopting suitable storage and feeding procedures. The amounts of fumigant actually consumed accounted for 50-70per thousand of the residue initially present in the mash. Triglyceride accumulation in the liver was the most sensitive sign of chronic poisoning with carbon tetrachloride and was apparent after only 5 wk of treatment with a daily dose of about 1per thousand of the LD50. Ethylene dichloride caused only a slight increase in liver fat at very high doses. Carbon tetrachloride and ethylene dichloride were each administered to rats for 2 yr in fumigated mash at levels below the obviously harmful ones. Growth fertility, reproduction and biochemical tests were used as criteria for establishing the no-effected levels. On the basis of these data, acceptable daily intakes of 10 mg/kg body weight for carbon tetrachloride and 25 mg/kg for ethylene dichloride are proposed. The respective tolerances are 100 and 250 ppm. The proposed tolerances in human food are discussed.