AbstractMethods have been developed for the analysis by gas‐liquid chromatography and thin‐layer chromatography of mecarbam and a number of its degradation products which result from oxidation and/or partial hydrolysis. In acid solution, mecarbam was found to be relatively stable but it decomposed more readily under alkaline conditions to giveO, O‐diethylhydrogen phosphorodithioate by fission of thesulphur‐carbon bond. At pH 9.2, the half‐life at room temperature was about 44 h. For residue analysis, a clean‐up procedure with Florisil was found to be preferable to one which employed alumina, as the latter caused cleavage of the ethoxycarbonyl group under certain conditions. Field trials with olives, oranges and pears showed that the parent pesticide, mecarbam, was the only significant detectable residue at any stage from treatment to harvesting, and that it tended to concentrate in the oil‐containing portion of the crop. Low levels ofO, O‐diethylS‐methylcarbamoylmethyl phosphorodithioate were also detected in residues from lucerne and from bean plants, and it was shown that this samemetabolite could be formed photolytically on filter paper or (morerapidly) on dock leaves.S‐(N‐Ethoxycarbonyl‐N‐methylcarbamoylmethyl)O, O‐diethyl phosphorothioate was detected only in bean plants and then, at a lev