Tribenuron methyl degraded rapidly in aerobic soil, forming the major metabolites IN-L5296, IN-A4098 and IN-00581 (found at >10% of applied radioactivity in laboratory studies). The rate of degradation was more rapid in acidic soils. Acid hydrolysis is considered to be the major degradation pathway. The DT50 values in soils of pH < 6 were 3 - 6 days, in soils of pH 6-7.4 was 10 days, and pH 􀁴7.5 were 12 - 20 days at 20 - 25°C in laboratory studies. The highest value will be used as a worst case in the calculation of predicted concentrations in soil. The phenyl moeity is mineralised via the formation and degradation of IN-00581, which occurred at a maximum of 11% at day 7 after application. Evolution of CO2 reached 54% after 90 days. Mineralisation proceeds more slowly for the triazine part via formation of IN-L5296 (max 83% at day 30 in Hawkins et al., 1995a), followed by subsequent formation and degradation of IN-A4098 (11% at day 120 in laboratory study, max 13% in German field study). Evolution of CO2 from the triazine ring reached 5.5% after 90 days. Formation of unextractable residues reached 18-32%, measured on days 120 and 270. In separate laboratory degradation experiments with the metabolites under aerobic conditions, IN-A4098 degraded in soil fairly rapidly, with DT50 of 22 – 39 days (mean 30 days). IN-L5296 and IN-00581 degraded more slowly, with laboratory DT50 of 112 – 220 days (mean 165 days) and 33 – 230 days (mean 131 days), respectively.