The biotransformation of nonylphenol was investigated in an agricultural soil treated with a mixture of 14C-labelled and unlabelled surfactant. It was then studied in soil samples amended with sludges spiked with the mixture of chemicals. Nonylphenol amount in all samples of soil and soil/sludge mixtures was 40 mg kg−1. In the soil free of sludge, the half-life of nonylphenol was found to be 4 d. When the soil was amended with sludge from the city of Ambares, France, it was about 16 d. In the soil amended with sludge from Plaisir, a 8-day lag phase was observed before the transformation starts, and nonylphenol half-life exceeded 16 d. In each case, nonylphenol transformation resulted in mineralization as well as stabilization of the chemical as bound residues within the soil. Further, some strains of filamentous fungi were isolated from the soil/sludge mixtures and identified to belong to the Mucor and Fusarium species. Most of them were able to efficiently transform nonylphenol in liquid cultures. In addition, the ligninolytic basidiomycete Trametes versicolor was able to catalyze partly the conversion of nonylphenol into carbon dioxide. Laccases purified from T. versicolor cultures are enzymes involved in nonylphenol oxidative coupling leading to oligomerization.