A 60-year-old man was admitted 1 hour after ingesting approximately 40 ml of Gramoxon (paraquat) in an attempt to commit suicide. Gastrointestinal lavage, compulsory urination, and direct hemoperfusion (DHP) were immediately performed to remove the paraquat. He was then administered Vitamin E and high dose methylprednisolone therapy to prevent lung injury. Chest roentgenogram on the 3rd day showed ground glass appearance in the outer zone of bilateral lung fields. Chest CT scans on the 9th day revealed a faint high density area in the same area, suggesting interstitial change. The shadows gradually improved and had disappeared on the 35th day after admission. Serum superoxide dismutase (SOD) activity, measured by electron spin resonance spectroscopy, was undetectably low until the 22nd day, and then increased into the normal range. It was suggested that SOD was consumed to neutralize the paraquat toxicity. Serum SOD activity changed according to the paraquat activity, and was a useful indicator of paraquat toxic activity. He was discharged without any symptoms 50 days after admission.