The aerobic degradation was reflected by the oxidation of the alkyl side chain to a carboxylic acid and also the oxidation of the cyano group to a carboxylic acid. The rate of degradation of the a.s. was calculated using linear regression assuming first order kinetics. The DT50 were 192, 465 and 574 days The levels of major metabolites were 0.2-9.2% at day 120. A maximum level of 10.2% was reached at day 76 in LUFA 3A soil. The major unknown peak was shown to contain 4 distinct components. The largest component (6% AR) was identified as the butyric acid of myclobutanil a second metabolite (2% AR) was identified as butyric diacid metabolite of myclobutanil; the other 2 metabolites could not be identified. Mineralization accounts for 0.2-1.7% AR at day 120. Bound residues account for 4.1-15.9% AR at day 120. Further analysis of the bound residues at day 120 showed that 0-7.7%, 2.1-10.6% and 1.1-4.7% of the applied radioactivity was associated with the humin (irreversibly bound), fulvic acid and humic acid fractions, respectively.