During laboratory studies of aerobic incubation at 20°C in four soils (pH 5.8-7.2, %OC 0.22-2.62), Spirodiclofen degraded with DT50s of 1.1-13 days and DT90s of 3.8-44 days (1st order). An experiment in one of four soils showed that there was no effect of the dose on degradation rate. Major metabolites exceeding 10% AR were BAJ 2740-enol (max. 14.5-51.9% AR on day 2-9), BAJ 2740- ketohydroxy (max. 8.4-44.4% AR on day 3-30), BAJ 2740-dihydroxy (max. 1.0-16.4% AR on day 2- 120) and 2,4-dichlorobenzoic acid (max. 2.0-39.6% AR on day 3-120). The metabolite BAJ 2740- lactide never accounted for >3.0% AR. Up to nine unidentified fractions were detected, none individually accounting for >5.9% AR. DT50s for major metabolites at 20􀁱C were 1.9-9.8 days (BAJ 2740-enol), 0.6-26 days (BAJ 2740-ketohydroxy), 3.8-49 days (BAJ 2740-dihydroxy) and 3.5-11 days (2,4-dichlorobenzoic acid). Mineralisation of Spirodiclofen was significant (22.5-93.1% AR by day 120 for dihydrofuranone-label in 4 soils, 69.1% AR by day 119 for cyclohexyl-label in 1 soil). Non-extractable residues formed from the dihydrofuranone-label were low (maximum 8.0-14.4% AR on day 13-120 for dihydrofuranone-label in 4 soils). An experiment in one soil showed that slightly higher levels of non-extractable residues were formed from the cyclohexyl-label (maximum 19.6% on day 55) than from the dihydrofuranone-label (maximum 10.1% on day 120). Aerobic metabolism of Spirodiclofen in soil proceeds by ester-cleavage to give BAJ 2740-enol. BAJ 2740-enol is metabolised to BAJ 2740-ketohydroxy by oxidation of the dihydrofuranone ring. BAJ 2740-lactide and BAJ-2740-dihydroxy are formed from BAJ 2740-ketohydroxy by rearrangement and reduction, respectively. Hydrolytic or oxidative ring-opening leads to the formation of 2,4- dichlorobenzoic acid from the former 3 metabolites. The ultimate and major breakdown product is CO2 together with low levels of non-extractable residues.