Studies in our laboratory have demonstrated that bis(chloromethyl)ether (BCME) and chloromethyl methyl ether both alkylating agents, are potent respiratory tract carcinogens. It has further been observed that low levels of bis(chloromethyl)ether may be formed by the gas phase reaction of formaldehyde and hydrogen chloride. Our limited preliminary work suggests that the combined vapors at low levels of 10 ppm of each gas causes carcinogenic effects in rats. Since both of these chemicals are extensively used, of en in close proximity, this represents a potential hazard of great magnitude. The proposed study is designed to: 1) Determine the carcinogenic effects of these combined exposures, 2) Determine possible carcinogenic effects of these chemicals when given separately, and 3) Determine the promoting or cocarcon genic effects of hydrogen chloride on formaldehyde, and 4) Determine the level of alkylating activity of BCME and other alkylating agents present in the combined atmosphere of formaldehyde and hydrogen chloride. The study involves 700 Sprague Dawley rats, divided into seven groups. Animals will be exposed by inhalation in the following manner: 6 hour/day, 5 days/week to: 1) formaldehyde and hydrogen chloride at the 10 ppm level, mixed and pre-mixed; 2) Formaldehyde or hydrogen chloride given separately at 10 ppm; 3) formaldehyde and hydrogen chloride on alternate days at 20 ppm each; 4) Air sham-exposed and untreated controls.