Four soils in two separate studies were analysed in the laboratory using appropriately 14C-radiolabelled proquinazid, from which the route of degradation can be investigated. These studies were conducted in accordance with relevant guidelines and GLP. The studies were performed on aerobic soils at 20° C in the dark. A range of soil types were used, from the UK, France, Germany and the USA. During the course of the study, degradation of proquinazid was variable, and the calculated DT50 values ranged from 39.5 to 449 days. Relatively high levels of metabolites were found in each soil, and three individual metabolites have been identified. The principal metabolite formed was IN-MM671, which had a maximum concentration ranging from 27 % AR in the UK soil, to as high as 65 % AR in the French soil, 120-122 days after application. Two other metabolites were also found. These were IN-MM986, which reached up to 2% AR at 120 days, and IN-MM991, which reached a maximum of 7 % AR after 120 days. IN-MM991 never occurred at 5% AR or greater on two consecutive timepoints within 120 days, but was increasing at 120 days in one soil. Unextracted residues in the four soils accounted for between 6 and 15 % AR at 120 days. Volatiles were low throughout the course of the study in all soils. Volatiles other than CO2 were < 1 % AR in all soils. CO2 concentrations at 120 days after application ranged from 0.1 % AR to a maximum of 10 % AR in the French soil. Thus it appears that proquinazid does not undergo significant mineralization under aerobic conditions. There is no obvious reason for the higher level of mineralization in the French soil.