Laccase from Coriolus hirsutus catalyzes the oxidative condensation reaction between 3-methyl-2-benzothiazolinone hydrazone and 3-dimethylaminobenzoic acid to form a blue indamine dye. Optimum enzyme activity in this reaction occurs at pH 5. The rate of formation of the dye is linear with time until an equilibrium is reached The absorbance values at equilibrium depends on the concentration of reactants, although maximum absorbance at equilibrium is obtained at a final concentration of 2.0 . 10(-3) M 3-dimethylaminobenzoic acid and 4.8 . 10(-5) M 3-dimethyl-2-benzothiazolinone hydrazone in the reaction mixture. The laccase-catalyzed condensation occurs in the absence of hydrogen peroxide contrasting with the reaction in the presence of horseradish peroxidase. When laccase is present, pretreatment of solutions with catalase does not inhibit dye formation, whereas dye is not formed when peroxidase alone is present.