A previously described linked set of lignin peroxidase-encoding genes (Lpo) from Phanerochaete chrysosporium (P.c.) ME446 is not expressed under standard growth conditions for ligninolytic activity. However, a single unlinked Lpo gene, not previously described in P.c. strain ME446, is expressed. The transcription start points of this gene are mapped and the gene is assigned to a genetic linkage group by the use of restriction-site polymorphism segregation analysis. No transcripts from Lpo-related genes, including that normally expressed in ME446, could be detected within RNA extracted from three nonligninolytic mutant strains, but a hyper-ligninolytic strain showed an increased level of Lpo expression. This increase is due to expression of additional Lpo genes, rather than to an increased level of transcription from the normally expressed sequence.