Acute oral toxicity was evaluated in groups of 5 male and 5 female Sprague-Dawley rats administered hexachlorocyclopentadiene in corn oil by gavage at a level of 1.26, 1.60 or 2.00 g/kg. Mortality was observed in 1 male and 2 females in the 1.26 g/kg group, 3 males and 5 females in the 1.60 g/kg group and in all animals in the 2.00 g/kg group. The LD50 was determined to be 1.4 (1.2-1.5) g/kg for males and females combined, 1.5 (1.3-1.7) g/kg for males only and 1.3 (1.0-1.5) g/kg for females only. Clinical observations included piloerection, abnormal posture and gait, lethargy, decreased respiration, ptosis, pallor of the extremities, diarrhea and prostration. Necropsy revealed nothing unusual.