The voltammetric behavior of dihydroxybenzene isomers was studied with glassy carbon electrodes modified with multi-wall carbon nanotubes. In 0.1 mol L-1 HAc + NaAc buffer solution (pH 5.5), the modified electrode showed a good electrocatalytic response towards dihydroxybenzenes. The peak currents increased significantly and their oxidation potentials shifted negatively. Through a derivative technique, the three oxidation peaks of dihydroxybenzene isomers can be separated, thus the method can be applied to direct simultaneous determination without previous separation. The linear calibration ranges were 2 x 10(-6)-1 X 10(-4) mol L-1 for hydroquinone and catechol, respectively, and 5 x 10(-6) to 8 X 10(-5) mol L-1 for resorcinol, with detection limits of 6 x 10(-7), 6 x 10(-7) and I X 10(-6) mol L-1, respectively. This method has been applied to the direct determination of dihydroxybenzene isomers in artificial wastewater, and the recovery was from 92% to 104%. (C) 2004 Elsevier B.V. All rights reserved.