The route of degradation of cycloxydim in soil under dark aerobic conditions at 20 ± 2ºC or 22 ± 2ºC was investigated in three studies. A total of six soils were investigated covering a range of pH (5.4 – 7.5) and organic carbon (0.52 % - 3.5 %). In the first two conducted metabolism studies it was not possible to seperate the peaks in each cluster and therefore a third study was conducted to investigate the metabolism of cycloxydim. The data on the parent were considered as valid and were used as further information. The aerobic metabolism studies showed that cycloxydim was oxidized at the sulfur atom immediately after application to the soil. The predominant metabolite is the corresponding sulfoxide BH 517-TSO, which occurs with a maximum of 90.4 % AR 1 day after application. BH 517-TSO degrades to a certain extent to the oxidation product BH 517-TSO2 (max. 9.5 % AR after 14 days). The active substance and these two metabolites contain the ethoxyimino group. This ethoxyimino group includes a C=N double bond where an E/Z isomerization occurs frequently and easily. It was shown by dynamic NMR studies that the ratio of the isomers depends on the physical state of the compound and the polarity of the solvents. In acidic solution in polar protic solvents, the E form isomerizes to the Z form until equilibrium is reached after several hours. In alkaline solution, no E/Z isomerization was observed. It was not possible to isolate the Z isomer as it seems to be on a higher energy level. Therefore, all tests were started with the E isomer from the solid state or in formulation. This approach seems to be appropriate as the tests mirrors the environmental conditions. For this reason all calculations were carried out with the sum of both isomers. Six additional metabolites were formed under aerobic soil conditions. All these metabolites, BH 517-T1S (max. 0.7 % AR), BH 517-T1SO (max. 4.2 % AR after 7 days), BH 517-T1SO2 (max. 2.6 after 60 days), BH 517-T2S (max. 0.3 % AR at day 0), BH 517- T2SO (max. 8.1 % AR after 30 days) and BH 517-T2SO2 (max. 9.9 % AR after 90 days) were formed in amounts < 10 % AR. The final product of degradation was CO2 which was formed in amounts up to 40-60 % AR in the investigated soils. Only moderate amounts of soil bound residues were formed; not more than 30% of the applied radioactivity was found to be non-extractable.