Decolorization of dyes belonging to various groups was carried out using novel free radicals-generating systems consisting of Cu(II), organic acids and hydrogen peroxide. Among the organic acids tested, succinic acid was the most effective. A 24 h incubation in the presence of 10 mM Cu(II), 200 mM succinic acid, and 100 mM H2O2 resulted in 85-95% decolorization of Remazol Brilliant Blue R (RBBR), Reactive Blue, Poly B-411, Chicago Sky Blue, Evans Blue and Methyl Orange. The replacement of Cu(II) with other transition metals was less effective but 78% decolorization was detected in the case of Co(II) and succinic acid. The decolorization is due to the formation of hydroxyl radicals, formed during the decomposition of H2O2 by the metal-ligand complex. (C) 2003 Elsevier B.V. All rights reserved.