Advanced oxidation of the commercially available reactive dyestuffs Remazol Black B and Remazol Turquoise Blue G 133 in aqueous solution with TiO2-mediated photocatalytic and photoinduced and dark Fenton/Fenton-like reactions has been studied. Initial decolourization rates, effectiveness in removal of UV254 (nm), COD as well as TOC were compared and evaluated. It was found that all advanced oxidation systems were capable of completely decolourizing the azo dye Remazol Black in feasible treatment times and at concentrations typically found in dyehouse effluents, whereas COD and TOC removal efficiencies ranged between 77-98% and 51-86%, respectively. Photo-Fenton's oxidation gave the best decolourization reaction, which proceeded 20 times faster than TiO2-mediated photocatalytic oxidation. Moreover, photocatalytical treatment of Remazol Black followed the empirical Langmuir-Hinshelwood kinetics in the concentration range 25-100 mg/l. However, none of the advanced oxidation systems was effective in the degradation of the copper phthalocyanine dye Remazol Turquoise Blue for which colour and COD removal was mainly attributable to adsorption on the photocatalyst surface or the coagulating effect of iron applied in the homogenous advanced oxidation reactions. (C) 1999 Elsevier Science Ltd. All rights reserved.