A method for simultaneous determination of 17 organochlorine and 9 pyrethroid pesticides in agricultural products by capillary GC with ECD detection was studies. The samples were extracted with acetone under acidic conditions followed by Florisil column clean-up and then injected into a GC-ECD. The organochlorine pesticides used in this study included unstable captan and captafol in the homogenized preparations of fruits and vegetables. Captan and captafol were also found to decompose in rice and wheat samples when the samples were allowed to stand after the addition of water. Addition of phosphoric acid to the samples was effective in preventing the decomposition of captan and captafol. Recovery of the pesticides investigated in this study was not decreased by the addition of phosphoric acid. Addition of phosphoric acid was also effective in removing interfering substances from onion extract. Recovery of organochlorine and pyrethroid pesticides from samples spiked at levels of 0.05-0.25 ppm by the proposed method was 51.4-100.8% for rice and wheat and 60.1-119.0% for vegetables.