Acute inhalation toxicity was evaluated in groups of 5 male and 5 female Fischer 344 rats exposed to Aerothene TT (1,1,1-trichloroethane) at actual concentrations of 15,523, 18,425, or 21,063 ppm for 4 hours. Mortality was observed in 3 females in the 18,425 ppm dose group and all animals in the highest dose group. The LC50 value was reported to be between 18,425 - 21,063 ppm for males and calculated to be 18,000 ppm (16,600-19,400 ppm 95% confidence limits) for females by the moving average method. Clinical observations included lethargy and unresponsiveness. Gross necropsy revealed clear facial soiling and visceral congestion.