Four groups of ten male and ten female albino rats were exposed for 6 hours per day, 5 days per week, for 4 consecutive weeks to either clean filtered air or 5.1, 48.2 or 460 (micro)/L of benzotrichloride (BTC) vapor. Gasping and dyspnea were observed in animals exposed to 48.2 and 460 (micro)/L BTC. All animals exposed to the 460 (micro)/L level either died or were sacrificed during the first study week. Animals exposed to 48.2 (micro)/L exhibited decreased body weight gain. There were no apparent effects observed in the hematology, clinical chemistry or urinalaysis data which could be related to the exposure conditions. Exposure related changes in the respiratory system were observed microscopically. The changes consisted of desquamation of the superficial lining cells of the bronchi and bronchioles. The nasal turbinates and trachea showed infiltrates of acute inflammatory cell loss and/or squamous metaplasia of the superficial epithelial cells.