Photolysis plays a major role for the degradation pathway and degradation rate. Major metabolites are formed in light but not in the dark. In laboratory studies in the dark the degradation of fludioxonil was relatively slow with DT50 ranging between 143 days and >365 days (best fit) depending on especially the initial concentration, while DT50 for field soil dissipation trials exposed to sunlight ranged between 7 days and 52 days. Soil photolysis studies in the laboratory showed initial DT50 values for the light exposed part of fludioxonil at approximately 1 day. As the intended uses of fludioxonil is both foliar spray and seed treatment the major role of photolysis regarding degradation of fludioxonil and formation of metabolites gives a big difference in the fate and behaviour between the two different intended uses. Aerobic degradation in laboratory studies in the dark resulted mainly in the formation of CO2 (0.59 to 11.1% AR (pyrrole-labeled) and 10.8 to 20.5% AR (phenyl-labeled) after 90 days at 20°C) and non-extractables (2.4 to 18.0% AR (pyrrole-labeled) and 17.3 to 19.4% AR (phenyl-labeled) after 90 days at 20°C). Only few fraction of metabolites in small amounts (total amount of metabolites: 0.3-8.4% AR) were detected. Due to the low concentrations of metabolies the isolation and identification was not performed. The low amounts indicate that potential metabolites were short living intermediates, compared to the half life of fludioxonil. The observed mineralisation rate supports this conclusion and demonstrates the importance of microbial processes in the degradation of fludioxonil and its metabolites. It also explains the absence of any significant amounts of metabolites in field soil dissipation studies without light exposure. The extent of transformation to bound residues and CO2 depend on the initial concentration of fludioxonil, the label position and the microbial activity of the soil. Both ring moieties are subject to metabolisation to carbon dioxide, but the extent of the mineralisation was faster and higher with the phenyl label compared with the pyrrol label.