Heterogeneous photocatalytic degradation of the pesticide Diuron (Nortox, 3-(3,4-dichlbrophenyl)-1,1-dimethylurea) was carried under laboratory conditions to evaluate the potential use of this technology for in situ remediation. Soil samples were spiked with three Diuron concentrations (10, 50 and 100 mg kg(-1)), loaded with catalyst TiO2 and exposed to solar light (22degreesS and 47degreesW, with an averaged intensity of 2 mW cm(-2) measured at 365 nm). Different catalyst loads (0, 0.1, 0.5, 1 and 2% w/w) were tested in Diuron contaminated soil (100 mg kg-1) for up to 120h of exposure. Both the catalyst and the Diuron concentration show no influence on the kinetics of the pesticide degradation. The effects of water (10% w/w) and Ca(OH)(2) (0.1% w/w) were also evaluated. Water increases the degradation rates, whereas the rise in the pH due to Ca(OH)(2) addition shows no measurable effect on the degradation. The photocatalytic treatment using TiO2 combined with solar light is shown to be very efficient in the destruction of Diuron in the top 4 cm of contaminated soil, with the degradation rate markedly dependent on the irradiation intensity.