Benzotrichloride (BTC) is used in the synthesis of benzoyl chloride and benzoyl peroxide. Epidemiological data suggest that BTC is a human lung carcinogen. In the present study, BTC was evaluated for its ability to induce lung adenomas in strain A/J mice. Four groups of 15 male and 15 female A/J mice were injected i.p. with either tricaprylin or BTC in tricaprylin three times a week for 8 weeks. BTC groups received doses totaling 1440 mg/kg, 719 mg/kg or 287 mg/kg. The mean number of lung tumors per mouse was 127 87 plus or minus 5.81, 43 plus or minus 2.44, and 17.73 plus or minus 1.09 in the groups treated with either 1440 mg/kg, 719 mg/kg, or 287 mg/kg, respectively. Tricaprylin-vehicle controls had a mean number of 0.46 plus or minus 0.15 lung tumors per mouse. Therefore, BTC produced a significant (P<0.001) and dose-related increase in the lung tumor response when compared to tricaprylin controls and is a potent carcinogen in the strain A mouse lung tumor bioassay. (Copyright (c) 1986 Elsevier Scientific Publishers Ireland Ltd.)