The kinetics of the photocatalytic degradation of 3-amino-2-chloropyridine, as a model compound for pyridine containing pesticides, in UV illuminated aqueous suspensions of TiO2 were investigated. It was found that mineralization to carbon dioxide, water, chloride, ammonia, and nitrate takes place during the process. The rate of degradation was studied by HPLC, ion chromatography and UV spectrometry, as well as by continuous potentiometric measurement of the rate of chloride generation and the pH change of the medium. It was found that the reaction in the investigated concentration range is of the zero-order in respect to 3-amino-2-chloropyridine degradation with the reaction rate constant 8.9 x 10(-6) mol/(dm(3) min) and adsorption coefficient 1.2 x 10(4) dm(3)/mol. HPLC analysis indicated that very few pyridine containing intermediates at low concentrations are formed during the process. Based on the obtained data a tentative reaction mechanism was proposed. Kinetics of the degradation were also monitored for direct photolysis, as well as for solar degradation in the presence and in the absence of TiO2. (C) 2003 Elsevier B.V. All rights reserved.