According to the statistics by the Ministry of Health on toxications due to drugs for agricultural uses, we have had incidents by organic chloride compounds for many years. In future, there is also a possibility to encounter chronic intoxications by the above compounds. We have relied on solely a close observation on clinical manifestations for its diagnosis. Understandably, there has been no proper treatments established up to now. Therefore, it is a very urgent demand in our community to establish the most reliable method detecting organic chloride substance. The author have tried to devise a simplified method to detect organic chloride substance, as quick as possible in peripheral blood, using an electron capture detector. Its principle was based on gas-chromatography. Results 1) It takes approximately one hour with petroleum-ether to extract organic chlorides in peripheral blood. This is a simplified and speedy method as compared to a conventional way which needs a complicated clean-up. 2) A minimal concentration of organic chlorides to be detected is 0.008ppm for Dieldrin, 0.003ppm Aldrin, 0.02ppm p,p'-DDT and 0.003ppm γ-BHC, indicating a significantly sensitive method. 3) It is feasible to extract various organic chlorides separately by combining several columns in a gas-chromatograph, i.e., 1.5% SE-30, 10% DC-200+15% QF-1 and 1.5% OV-17. The author, thus, has been able to produce an evidence that the above method is extremely useful for diagnosing the intoxication by organic chlorides. Using this method, a part of the dynamics in the intoxicated patients has been also clearified.