Aldicarb and its degradation products in water may be determined by highperformance liquid chromatography (WHO, 1991). When followed by post-column derivatization to form fluorescent compounds, this method has detection limits of about 1.3, 0.8 and 0.5 μg/litre for aldicarb, the sulfoxide and the sulfone, respectively (Foerst & Moye, 1985). Aldicarb and its oxidation products can also be determined as their nitrile derivatives by capillary gas chromatography with a nitrogen–phosphorus detector (Zhong et al., 1984).