A cellulolytic active oxygen species, hydroxyl radicals ((OH)-O-.), play a leading role in the erosion of wood cell walls by brown-rot and non-selective white-rot fungi. In contrast, selective white-rot fungi have been considered to possess unknown systems for the suppression of (OH)-O-. production due to their wood decay pattern with a minimum loss of cellulose. In the present paper, we first report that 1-nonadecene-2,3-dicarboxylic acid, an alkylitaconic acid (ceriporic acid B) produced by the selective white-rot fungus Ceriporiopsis subvermispora intensively inhibited (OH)-O-. production by the Fenton reaction by direct interaction with Fe ions, while non-substituted itaconic acid promoted the Fenton reaction. Suppression of the Fenton reaction by the alkylitaconic acid was observed even in the presence of the Fe3+ reductants, cysteine and hydroquinone. The inhibition of (OH)-O-. production by the diffusible fungal metabolite accounts for the extracellular system of the fungus that attenuates the formation of (OH)-O-. in the presence of iron, molecular oxygen, and free radicals produced during lignin biodegradation. (C) 2002 Elsevier Science (USA). All rights reserved.