The lignin mineralization rate in cultures of Phanerochaete chrysosporium increases with lignin peroxidase concentration up to 20 nkat ml -~. At higher concentrations the rate of lignin mineralization decreases with increasing lignin peroxidase concentration. The amount of mycelium is not a limiting factor for lignin mineralization at high exocellular lignin peroxidase concentrations. Cultures that contain lignin peroxidase in association with the mycelium as pellets and no free exocellular enzyme induce a lignin mineralization rate equivalent to cultures reconstituted with washed pellets supplemente d with 15 nkat m l -~ of exogenous free enzyme. These results show that although lignin degradation by lignin peroxidase seems to be facilitated when lignin peroxidase is localised on the surface of the mycelium, free exocellular lignin peroxidase can also efficiently enhance mineralization of lignin by P. chrysosporium.