Abstract: Fifty cases of DDVP poisoning outpatients from six hospitals around Hangzhou district over the period from April 1988 to octorber 1991 were collected consecutively for lethal blood concentration study.Blood samples were detected with gas chromatography.The probabilites were analysised with BIBs method.As the results,the linear regressive equation of the death probability was as follows: Yr=2.832+1.305lgX and of the coma rate: Yc= 3.554+1.558lgX The LC_(50)and CC_(50)were 45.80mg/l and 8.48mg/l respectively.As the death rate was influenced by therapy,its natural death probability has been discussed and estimated from above two formulas as follows: Ye=3.161+1.421lgX and the LCe50 is calculated as 19.69mg/l.