The hemoprotein ligninase of Phanerochaete chrysosporium catalyzes, in the presence of H2O2, a variety of seemingly different oxidations in lignin and lignin model compounds. Here we show that the enzyme also catalyzes the oxidation of various methoxybenzenes. ESR spectroscopy shows that the compounds are oxidized to aryl cation radicals. These decompose, evidently by H2O addition. Thus, 1,4-dimethoxybenzene is converted to p-benzoquinone and methanol. We propose a unified mechanism, based on formation of aryl cation radicals, to explain the various reactions catalyzed by the ligninase.