One study was conducted on the aerobic degradation of diuron in soil by Mackie & Hall (1993). The range of mean total recoveries of applied radioactivity from the five incubation groups (3 soils) was 89% to 99% during the test period. Extractable radioactivity recovered from the soil declined as the incubation progressed, but varied with each of the incubation groups (range after 100 days incubation: 44 to 84%). A concomitant increase in the non-extractable residues from each incubation group was observed (range after 100 days incubation: 12 to 44%). Volatile traps, designed to collect radiolabelled carbon dioxide (14CO2), from loamy sand and sandy loam (20°C, 35% water holding capacity) were analysed and levels of 14CO2 in the range 5 to 7% were detected following 100 days incubation. Degradate profiling, using thin layer chromatography, indicated that 14C-diuron was the principal radiolabelled component detected in sandy loam (20°C, 70% water holding capacity) at 0 hr, accounting for 91% of the applied radioactivity. As the incubation progressed, levels of DCPMU increased, accounting for 33% at 100 days post-application. Further degradation of DCPMU to DCPU and DCA also resulted in 4 and 2% at 100 days, respectively. The profile of degradation products for the other soil types and incubation conditions were similar to that for sandy loam (20°C, 70% water holding capacity), although the extent of degradation varied. Levels of diuron remaining in loamy sand, sand, sandy loam at 10°C and sandy loam at 35% water holding capacity at 100 days post-application were 3, 51, 56 and 8% respectively. The calculated DT50 for soils incubated at 20°C and 70% water holding capacity ranged between 20 and 119 days. In conclusion, the rate of degradation of 14C-diuron varied with soil type, decreased with reduced temperature and increased with lower soil moisture content.