The purpose of this study was to evaluate the inhalation toxicity of 1,1,1,3-tetrachloropropane (TCP), an intermediate in the production of chlorinated silicone fluids. Male and female Sprague-Dawley rats were exposed 6 hr/day, 5 days/week, for 90 days to TCP at concentrations of 0, 25, 75, or 225 ppm (Phase I study) and to 0, 1, 5, or 10 ppm (Phase II study). Phase II of the study was conducted because a no-observed-effect level was not achieved in Phase I. No animals died during the study. Clinical signs of toxicity included oral, nasal, and/or ocular discharge. No statistically significant differences were observed in either body weights or food consumption between exposed and control animals. Clinical pathology did not indicate any treatment-related effects. Absolute and relative liver and kidney weights were increased in male and female rats exposed to 225 ppm TCP, and heart weights were increased in male rats exposed to 225 ppm TCP. The liver and heart weight changes were supported by the findings of microscopic lesions in these organs. These lesions consisted of multifocal/focal myofiber degeneration necrosis with adjacent chronic myocarditis in the heart and multifocal single-cell necrosis in the liver parenchyma. The liver lesions had essentially resolved at the end of a 28-day recovery period but the heart lesions were still present in male rats in the recovery group exposed to 225 ppm TCP. No treatment-related effects were observed in animals exposed to 1, 5, or 10 ppm TCP.(ABSTRACT TRUNCATED AT 250 WORDS)