The degradation of captan residues during the processing of apple to sterilised purée was investigated using laboratory small-scale processing (125 °C for 20 min and pH 4.0). [14C]-cyclohexene ring-labelled captan was completely degraded, mainly to tetrahydrophthalimide (96.5%). Other minor products such as tetrahydrophthalic acid (0.3) and tetrahydrophthalamic acid (0.2) were identified by HPLC and mass spectrometry. [14C]-trichloromethylthio-labelled captan was completely degraded essentially to [14C]CO2 (77%) accompanied by small amounts of [14C]CS2 (2%). Thiophosgene was not detectable. Approximately 11.5% of the radioactivity was non-extractable and was believed to result from the reaction of the trichloromethylthio moeity with endogenous compounds of the apple, e.g. protein. The results were compared with those obtained in buffer medium mimicking the same process.