A method is described for the determination of oxamyl residues in crops and soils by gas-liquid chromatography. Oxamyl is extracted with dichloromethane or acetone -dichloromethane and is separated from interfering co-extractives by chromatography on a Florisil column. It is then determined by gas-liquid chromatography using on-column reaction with trimethylphenylammonium hydroxide, the derivative so formed being determined by a flame-photometric detector operated in the sulphur mode. Approximately 0.5 µg of oxamyl can be detected in a 50-g sample.