The adsorption of monocrotophos (MCP) was carried out over HY, Hbeta and H-ZSM-5 zeolites. The adsorption of MCP follows the order HP > HY > H-ZSM-5 and hence HP was chosen as the support for TiO2. The photocatalytic degradation of MCP on TiO2 and TiO2/Hp catalysts was studied using low-pressure mercury lamps (lambda = 254 nm) in a slurry reactor. The HP supported TiO2 showed higher degradation efficiency than bare TiO2. This higher activity of the supported catalyst is due to the greater adsorption of MCP on the support and capability of support to delocalise the conduction band electrons of excited titania. Total organic carbon (TOC) analysis indicates complete mineralisation of MCP The relative photonic efficiency was calculated for TiO2 and TiO2/Hp. (C) 2004 Elsevier B.V. All rights reserved.