The white rot fungus Phanerochaete chrysosporium has the largest cytochrome P450 contingent known to date in fungi, but the study on the function of these P450s is limited. In this study, induction of functional P450 in P. chrysosporium was first shown and P450-mediate degradation of benzoic acid was demonstrated in this fungus. Carbon monoxide difference spectra indicated significant induction of P450 by benzoic acid, m-chlorobenzoic acid, p-chlorobenzoic acid and n-hexane, and showed the effect of inducer concentration and nutrient condition on the induction of P450. The high contents of P450 in the microsomal fractions facilitated the study on the function of P450. While the n-hexane-induced P450 could not interact with benzoic acid, the microsomal P450 induced by benzoic acid produced type I substrate binding spectra upon the addition of benzoic acid. The benzoic acid degradation by the microsomal P450 was NADPH-dependent at a specific rate of 194 +/- 14 min(-1), and significantly inhibited by piperonyl butoxide (a P450 inhibitor). However, inhibition of benzoic acid degradation by piperonyl butoxide was slight or not detectable in the cultures of this fungus, suggesting presumable involvement of other enzyme in benzoic acid degradation. The extracellular ligninolytic enzymes, lignin peroxidase and manganese-dependent peroxidase, were not involved in initial metabolism of benzoic acid under the test conditions.