Acute oral toxicity was evaluated in groups of 5 male and 5 female Charles River CD-1 mice administered single doses of hexachlorocyclopentadiene as a solution in corn oil by oral gavage at levels of 21.5, 46.4, 100, 215, 464, 1000 and 2150 mg/kg of body weight. Mortality was observed in 1 female in the 46.4 mg/kg dose group, and all 10 animals in both the 1000 and 2150 mg/kg dose groups. The LD50 value was calculated to be 679 mg/kg (618-747 mg/kg 95% confidence limits) by the moving average method. Clinical observations included diarrhea, hypoactivity, decreased limb tone, ataxia, and ptosis. Gross necropsy findings were notreported.