Coriolus hirsutus pellets grown in a melanoidin-containing medium produced extracellular H2O2 up to 43 mu M. However, nonenzymatic decolorization of melanoidin by H2O2, which has been previously reported, seemed very little in the fungal culture. The culture fluid contained two extracellular peroxidases, a manganese-independent peroxidase (MIP) and manganese peroxidase (MnP). Since both MIP and MnP showed melanoidin-decolorizing activities in the presence of H2O2, it was concluded that melanoidin decolorization in the C. hirsutus culture involved the production of extracellular H2O2 and the peroxidases.