1. I discuss the following aspects of Phanerochaete chrysosporium ligninase, the enzyme that has been shown to degrade a number of lignin-model compounds, and environmentally significant polycyclic aromatic hydrocarbons and polychlorinated phenols. 2. The primary mode of oxidation involves formation of a cation radical, which undergoes either hydrolysis or carbon-carbon bond cleavage. 3. In the presence of reducing substrate such as oxalic acid, ligninase has reductive activity that has been shown to be responsible for radical-mediated degradation of halogenated chemicals. 4. Electron spin resonance technique can be used to monitor the cation radical and other radical formation during ligninase-mediated degradation of lignin-model compounds and other chemicals.