The main metabolites formed from Iprodione and Procymidone during the composting process have been isolated and identified by HPLC-DAD-MSD. After addition of the fungicides to the composting pile, we monitored the reaction of the two analytes and the formation of their degradation products for eight months. We verified the nature of the metabolites by comparison with those hypothesised in the literature and by comparison with the behaviour of an abiotic process in aqueous acetonitrile pH 6 and at 35 degrees C. After taking into account the different kinetic behaviours of the fungicides on degradation in compost and hydro-organic solution, breakdown pathways are proposed for biodegradation.