White-rot basidiomycetes produce extracellular lignin peroxidase, manganese peroxidase and laccase, which catalyze the degradation of aromatic xenobiotics via free-radical intermediates into CO(2) and H(2)O. However, insufficient data are available on the dependency of degradation rate constants on the chemical structure of xenobiotics. This study examines the degradation rates of bisphenol compounds BPA, BPE and BPF by a white-rot basidiomycete, Coriolus hirsutus IFO 4917. BPA, BPE and BPF have respectively 2, 1 and 0 methyl groups bonded with the central carbon located between their two phenol groups. Experimental analysis was performed assuming that the degradation of these bisphenol compounds follows first-order reaction kinetics. On this basis, the degradation rate constants for BPA, BPE and BPF were 3.90, 3.62 and 2.81 h(-1), respectively, showing a positive relation with the numbers of methyl groups. Considering that BPF is composed of phenol and p-cresol, the degradation rate constants of phenol and p-cresol by C. hirsutus IFO 4917 were further measured and found to be 2.92 and 1.05 h(-1), respectively. Structurally, p-cresol has a methyl group substituted into the para-position of phenol, and its degradation rate was higher than that of phenol. This observation leads to the conclusion that the substitution of an electron-donating methyl group into the benzene ring promotes the biodegradation of xenobiotics by white-rot basidiomycetes via a radical reaction.