Lignin peroxidase (LiP) plays an active role in the biodegradation of lignin and phenolic structures resembling lignin. The role of other enzymes in the biodegradation of recalcitrant compounds, e.g. manganese(II)-peroxidase, is uncertain. Solid manganese(IV)oxide addition improved the production of manganese(II)-dependant peroxidase (MnP) and H202 and increased the rate of biodegradation of Aroclor 1254 in a nitrogen-limited medium by the white rot fungus Coriolus versicolor. MnP activity was detected 48 h after the addition of Mn02 to the cultures and was absent in cultures that did not receive Mn02. The rate of Aroclor 1254 removal by C. versicolor was influenced by the concentration of Mn02. 34.5 mM concentrations only increased the H202 production. Removal of Aroclor 1254 in the absence of Mn02 still took place which implied the presence of (LiP) or nonspecific absorption. The cultures containing 57.5 mM Mn02 removed ca. 84% of the initial 750 mg 1-1 Aroclor in 6 days of incubation. Cultures with no Mn02 and 34.5 mM removed 79 and 76%, respectively. Cultures with MnP or LiP as the dominant enzyme species removed penta- and hexachlorobiphenyls at a slower rate than tri- and tetrachlorobiphenyl.