Groups of five male rats and five female rats were exposed to target concentrations of 3400, 2250, 1500, 563, 282, or 70 mg/m(sup 3) chlorosulfonic acid (CSA) for one hour and then held for 14 days of observation. CSA caused clinical signs of respiratory and eye irritation at all but the two lowest exposure concentrations. Mortality was observed during the observation period at the three highest dose levels. Gross and histopathologic changes observed at these dose levels included lung hemorrhage, enlarged livers, pale and small spleens, small thymuses, degenerative and inflammatory changes of the respiratory tract, liver hypertrophy, and degenerative changes in the spleen and thymus. With the exception of clinical signs of respiratory irritation, no treatment-related effects were observed at the three lowest dose levels. The one-hour LCm value was approximately 926 mg/m3. The test material has been used internally and sold as a pure chemical.