A lifetime carcinogenicity study was carried out in Wistar rats, with a mixture of the following halogenated hydrocarbons: trichloromethane, tetrachloromethane, monobromodichloromethane, trichloroethylene, tetrachloroethylene, 1,2-dichlorobenzene, 1,3,-dichlorobenzene, 1,4,-dichlorobenzene, 1,2,3,-trichlorobenzene, 1,2,4,-trichlorobenzene, 1,3,5-trichlorobenzene. From this mixture 0.22, 2.2, or 22 mg was added per liter drinking water representing concentrations being three orders of magnitude higher than found in several water wells. Most of the changes found in body weight, hematology and pathology correlated with intercurrent diseases or were in accordance with background pathology. With respect to incidence and time of occurrence of tumors, no significant differences were found between the control and the high dose group when lifespan correction was applied. Thus it is concluded that in the present study no significant toxic or carcinogenic effects are induced by lifetime exposure of rats to a mixture of volatile halogenated hydrocarbons in the drinking water.