Under aerobic conditions (20°C and 40% MHC), the degradation of fluazifop-butyl was studied on 6 soils, by applying 14C- pyridyl or 14C- phenyl – labelled substance on soil samples. In fact, the results from 2 soils were discarded, due to the conditions of conservation of these soils (too long storage period, resulting in a low bioactivity). For all aerobic studies performed with non-sterile soils, whatever the label, the total recovery of radioactivity ranged from 87 to 136% with an overall median recovery of 96%. The maximum measured CO2 amounts were 9.6% of recovered radioactivity (pyridyl- label) and 26.2% (phenyllabel) after 84 days, respectively 18.8 and 32.2 % of RR after 168 days. Under sterile conditions, the mineralization (0.4% RR after 84 days) and the levels of unextracted residues were low (5.8% RR after 84 days). The parent was rapidly degraded. The main route of degradation is hydrolysis, bio-activated. First, the acid derivative, 2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy]propionic acid (fluazifop, compound 2), was rapidly formed, with a maximum 83.4 % of RR, after 2 days of incubation. The degradation of fluazifop was dependant on microbial activity of the soil and was slower under sterile conditions. The metabolite 5-trifluoromethyl-pyrid- 2-one (compound 10) was derived from the pyridyl moiety, with a maximum 25.1% RR at 84 days, later decreasing. The metabolite 2-(4-hydroxyphenoxy)-5-trifluoromethyl pyridine (compound 4) which could be detected with both labels, was always minor (3.3% after 21 days), except once under low temperature conditions (12.9% RR after 84 days at 10°C). Besides these compounds, remaining unidentified compounds were extracted and partitioned, but not quantified. The total of these compounds ranged from 7.8 to 35.1% RR after 84 days, and from 12 to 46% RR after 168 days. According to the notifier, no individual unidentified is above 10%, but an additional analysis and report for these unidentified residues is required. Maximum unextracted residues were measured in Gore soil, 55.4% RR (equivalent to 53.4% AR) (phenyl label) after 84 days, later decreasing. Further extraction and fractionation of unextracted residues was conducted in some samples. None of the radioactivity associated with humin, fluvic acid or humic acid exceeded 10% of applied radioactivity. Clarifications should be given about the storage conditions of the samples and the dates of analysis.