Under conditions of either 20 C and 40% MWHC or 25 C and 75% of 1/3 bar in the dark under aerobic conditions, pinoxaden (NOA 407855) degraded very rapidly with DT50 values of < 2days. Two major metabolites were formed. The principal metabolite was NOA 407854 (M2), which formed maximum observed concentrations of 10.8 - 89.74 % AR at between 1 - 3 days after application; the lowest value was unusually low, maximum observed formation generally being in excess of 50%, and this could have been related to a low microbial biomass on the particular soil. However the reason for this low value is not known. NOA 407854 (M2) forms by loss of pivalic acid from the parent compound; kinetic analysis indicates that 100% of pinoxaden (NOA 407855) is converted to NOA 407854 (M2). This metabolite then forms the metabolite NOA 447204 (M3) by hydroxylation of the pyrazole ring. NOA 447204 (M3) formed maximum concentrations of 5.4 - 30.6 % AR at times between 7 and 120 days after application of the parent compound. In some cases, the maximum concentration was reached at the end of the study. Kinetic analysis indicated that 10.5 – 35.2% of NOA 407854 (M2) was converted to NOA 447204 (M3). A supplementary study on one of the soils conducted under aerobic sterile conditions indicated that degradation of pinoxaden (NOA 407855) is not specifically dependent on microbial activity in soils, although it is possible that degradation under sterile conditions is very slightly slower compared to those under non-sterile conditions. However, it is likely that the degradation is mostly abiotic. It is also clear that degradation of metabolite NOA 407854 (M2) is principally microbially mediated, there being relatively little degradation from the peak formation of 92.6% at 14 DAT until the study end at 120 DAT (85.1% AR). Unextracted residues accounted for 27.8 – 63.4 % AR at 100 - 120 days, the majority of this associated with the humin or fulvic acid fraction. Mineralisation was significant during the course of the study in most soils. CO2 at 100 – 120 days after application ranged from 4.3 - 47.6 % AR.