Laccase is a multi-copper oxidase that can decolorize textile dyes. There is increasing interest in its use to treat textile wastewaters which also contain auxiliary chemicals such as surfactants and salts. This investigation examines the effect of Merpol, a non-ionic surfactant, on the decolorization of Reactive blue 19, an anthraquinone dye, and on the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) by Trametes versicolor laccase. The results show that the surfactant had little effect on the enzyme or on ABTS oxidation which followed Michaelis-Menten kinetics. However, Reactive blue 19 decolorization was inhibited with increasing Merpol concentration. Spectroscopic analysis of the dye with Merpol and analysis of the kinetic data show that decolorization rates depended on an interaction between the dye and the surfactant. The proposed inhibition by a substrate depletion model in which the dye concentration decreases as a dye molecule binds to a surfactant molecule and/or is sequestered into micelles fits the data suitably and the model was validated by estimating the inhibition constant from independent saturation equilibrium binding assays. This study is the first to investigate the kinetic effect of a surfactant on the enzymatic dye decolorization and to show the depleting effect of Merpol on Reactive blue 19. (C) 2009 Elsevier Inc. All rights reserved.