To elucidate the fatal blood concentration of paraquat (Gramoxone), a contact herbicide, we investigated blood concentration of paraquat in 91 cases of paraquat intoxication. The blood paraquat concentration of 91 cases due to ingestion of paraquat was 0.9 $mu$g/ml-1023.5$mu$g/ml and has been subdivided according to survival time. 48 of 91 cases were identified survival time. In 34 of 48 cases died within a day after ingestion of paraquat, blood paraquat concentration was ranged from 2.3-636.61$mu$g/ml, and in 12 of 48 cases died 1-4 days after ingestion of paraquat, blood paraquat concentration was ranged from 0.9- 25.1 $mu$g/ml.