A series of 15 halogenated hydrocarbons of industrial and environmental importance were tested for carcinogenicity by chronic administration by one or more routes in Ha:ICR Swiss mice. Not all compounds were tested by the four routes of administration used. Allyl chloride, 1,2-dibromo-3-chloropropane, and vinylidene chloride were active as skin tumor initiators in the two-stage carcinogenesis assays; phorbol myristate acetate was used as a promoter. 1,2-Dibromoethane was the only compound that induced a significant incidence (P0.05: trichloroethylene, tetrachloroethylene, hexachlorobutadiene, chloroacetaldehyde, 1-chloropropene oxide (cis and trans), and trichloroethylene oxide.