Several studies have been performed under laboratory and field conditions to assess the behaviour of captan in soil. Laboratory studies indicated that the soil degradation of captan is very rapid under both aerobic and anaerobic conditions, with a DT50 of less than 1 day. Both the tetrahydrophthalimid ring and the trichloromethyl sidechain moieties of captan are eventually mineralised to carbon dioxide. Degradation of captan was observed under sterile conditions, indicating the importance of abiotic hydrolysis. Photolysis of captan was shown to be a minor degradation route of captan in soil. The principal initial degradate is THPI which undergoes cleavage of the imide ring to give THPAM. Other metabolites are generally at levels below 5% of the applied dose, apart from THCY (max. 20%) which is an important degradate under anaerobic conditions, although these conditions would not normally be encountered during the use of captan. THCY has been demonstrated to rapidly degrade to THPAM under aerobic conditions. THPAM is further degraded to CO2, which is incorporated into natural constituents of the soil. THPI and THPAM were found not to accumulate in soil, laboratory studies indicating that the DT50’s were less than 7 days. Recalculations using non-linear regression techniques gave estimated values of DT50 of 6.25 days for THPI and 6.4 days for THPAM.