In laboratory soil studies conducted at temperatures of 20 and 25°C, hymexazol is steadily degraded in a range of soil types under aerobic conditions. Aerobic degradation in soil did not lead to the formation of any major degradation products (i.e. 10% of applied radioactivity). Some minor degradation products were observed but these did not exceed a combined maximum total of 2.4% of applied radioactivity at any time and was likely comprised of multiple components. Degradation proceeded via the minor components and non-extracted residues to ultimate complete mineralisation to carbon dioxide. The level of non-extracted residue observed steadily increased initially, up to maximum levels of between 24 and 39% of applied radioactivity for each soil type between 18 and 90 days following treatment, but subsequently declined in all soil types. Further extractions indicated that substantial proportions of the non-extracted residue were deeply bound to the soil structure. The level of carbon dioxide evolved steadily increased throughout the study and comprised ca 40 to 65% after 50 days. No pH depencence of the degradation of hymexazol in soil was found. The DT50 values for the aerobic degradation of hymexazol were estimated to be between 13.7 and 31.5 days (four soils normalised at a temperature of 20°C). The rate of aerobic degradation was temperature dependant and at 10°C the DT50 value was increased to 101 days (the DT50 value for the corresponding soil at 20°C was 31.5 days), yielding an experimentally obtained Q10 factor of 3.2 corresponding to an activation energy of 80.0 kJ/mole.