This paper evaluates the degradation of a reactive azo dye, Procion Marine H-EXL, by catalytic wet hydrogen peroxide oxidation (CWHPO). The catalyst was prepared by ion-exchange, starting from a commercially available ultrastable Y zeolite. All experiments were performed on a laboratory scale set-up. The effects of different reaction parameters such as initial pH, catalyst and hydrogen peroxide concentrations on the oxidation of the dye aqueous solution were assessed. Apart from the conventional parameters, the toxic potential of the dye's degradation products was investigated using the bioluminescence, test. HPICE analysis was also performed to obtain detailed information on the resulting oxidation products (organic and inorganic anions). The results indicate that after only 10 min at 50degreesC, 20 mmol/l H2O2 and 1 g/l FeY11.5 the color removal was as high as of 97% at pH = 3 and 53% at pH = 5. More than 96% removal of the dye could be attained in 30 min at pH = 5, t = 50degreesC. 20 mmol/l H2O2 and 1 g/l FeY11.5 which corresponds to about 76% reduction of the initial COD and 37% removal of the initial TOC. A preliminary study of catalytic oxidation with hydrogen peroxide of the synthetic textile wastewater containing the specific dye is also presented. Leaching tests indicate that the activity of the catalyst is not due to leached iron ions, although an amount of 0.1-4.0 ppm of iron ions was found in aqueous solution. The catalyst allows almost total elimination of the dye and a significant removal of COD and TOC without the significant leaching of Fe ions. It was also observed that by using this catalyst, it is possible to extend the range of pH values for which Fenton-type oxidation can occur and no iron hydroxide sludge is formed. (C) 2003 Elsevier B.V. All rights reserved.