Benzo(a)pyrene was oxidized with crude and purified extracellular ligninase preparations from Phanerochaete chrysosporium. Both the crude enzyme and the purified fractions oxidized the substrate to three organic soluble products, namely benzo(a)pyrene 1,6-, 3,6-, and 6,12-quinones. These findings support the recent proposition that lignin-degrading enzymes are peroxidases, mediating oxidation of aromatic compounds via aryl cation radicals. The ligninase which was unstable in the presence of hydrogen peroxide could be stabilized by addition of 3,4-dimethoxy benzyl alcohol to the reaction mixture. The oxidation of benzo(a)pyrene was enhanced in the presence of this alcohol.