The ligninolytic enzyme system of Phanerochaete chrysosporium is able to decolorize several recalcitrant dyes. Three Lignin peroxidase isoenzymes, LiP 3.85, LiP 4.15, and LiP 4.65, were purified by preparative isoelectric focusing from the carbon-limited culture medium of P. chrysosporium. Based on amino terminal sequences, the purified isoenzymes correspond to the isoenzymes H8, H6, and H2, respectively, from the N-limited culture. The purified isoenzymes were used for decolorization of an azo dye, Crocein Orange G (COG). According to the kinetic data obtained, the oxidation of COG by lignin peroxidase appeared to follow Michaelis-Menten kinetics. Kinetic parameters for each isoenzyme were determined. The inactivating effect of ascending H2O2 concentrations on COG oxidation is shown to be exponential within the used concentration range. The best degree of decolorization of 100 mu M COG was Obtained when the H2O2 concentration was 150 mu M. This was also the lowest H2O2 concentration for maximal decolorization of 100 mu M COG, regardless of the amount of lignin peroxidase used in the reaction.