Chlorothalonil, 2,4,5,6-tetrachloroisophthalonitrile, is a broad-spectrum non-systemic fungicide extensively used on fruits, vegetables and other agricultural products worldwide. The maximum residue limit (MRL) for chlorothalonil in agricultural commodities ranges from 0.3 to 15 ppm. Its residues in crops have been analyzed commonly by GC with electron-capture detection (Valverde-Gareia, et al. 1993, Di Muceio A et al. 1993, Newsome and Collins 1989, EI-Nabarawy and Care), 1988, Lesser and Massil 1987, Bicchi et al. 1985) or HPLC with either UV Qongen et al. 1991) or photoeonduetivity and UV in tandem detection methods (Gilvydis and Waiters, 1988). More recently, immunoassays for chlorothalonil have been reported (Lawruk et al. 1993, Fitzpatrick et al. 1993a) and are applied primarily to water samples. Indepth reviews for the applications of immunochemical methods have been presented (Giese J 1993, Van Emon and Lopez-Avila 1992, Gazzazz SS, et al. 1992).