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A simple, rapid method to determine residues of chlorothalonil in green tea leaves was developed using a commercial chlorothalonil kit based on ELISA. Chlorothalonil in green tea leaves was measured using the chlorothalonil kit after being extracted by methanol or boiling in water and diluted with 10% methanol. Because the extracts of green tea leaves caused significant interference in the assay, a refinement method was examined. One nil of the extract from green tea leaves boiled in water or extracted with methanol was added to Oasis HLB (60 mg) and purified with 2ml of 80% methanol. After that, chlorothalonil on the HLB; was extracted with 2 nil of 100% methanol. It was suggested from the experiment that the component that was removed by column refinement was catechin, being the cause of interference with the chlorothalonil kit. As the results, average recoveries from the chlorothalonil-spiked green tea leaves were 86-113%, and the coefficients of variation were below 10% in most cases. The coefficient of correlation between the ELISA and GC/MS methods was 0.99. Analysis equivalent to GC became possible using ELISA, and we revealed that catechin is the main factor interfering with ELISA analysis, and established a refining process. It was confirmed that the methanol treatment method for HLB was useful for the rapid analysis of chlorothalonil residues in green tea leaves. (C) Pesticide Science Society of Japan