A synergistic effect of polyoxometalate and laccase (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) has been observed in the aerobic oxidation of a hydrazonaphthalene type colorant. The considerable increase in the decolorization rate of Solophenyl Blue GL dye with the new catalytic system composed by laccase and heptamolybdopentovanadophosphate heteropolyanion, when compared with the treatment with enzyme or heteropolyanion alone, was tentatively explained by the redox mediation action of the heteropolyanion. (C) 2000 Elsevier Science B.V. All rights reserved.