Abstract: Total cases of organophosphorous（ dichlorvos、 methamidophos、 dimethoate） poisoning outpatients from six hospitals during four years were collected consecutively for lethal blood concentration study. Blood samples were detected with gas chromatography. The probabilities of death, coma were analyzed with Bliss method and their linear regressive equations of probit were obtained respectively, their 50％ lethal concentrations(LC50) and 50％ coma concentrations(CC50) were calculated by the formulas above. As the death rate was influenced by therapy, its natural death probability has been discussed and estimated their natural LC50 were between the LC50 and CC50 themselves. Combined LC50 and CC50, their natural LC50 were calculated.

Key words: organophosphorous, Blood, gas chromatography, LC50, CC50