The kinetics of the photocatalytic degradation of 3-aminophenol (3-AP) has been investigated experimentally and theoretically. The reactions have been carried out in a batch-type photoreactor using TiO(2) P25 Degussa as the photocatalyst. The effects of the catalyst loading, the initial concentration of 3-AP and the electron accepters; H(2)O(2), K(2)S(2)O(8) and KBrO(3) on the degradation rate have been determined. With the intention of predicting the primary intermediates, geometry optimizations of the reactants, products and the transition state complexes have been performed with the semi-empirical PM3 method. The molecular orbital calculations have been carried out by an SCF method using RHF or UHF formalisms. Based on the results of the quantum mechanical calculations, the rate constants of the four possible reaction paths have been calculated by means of the Transition State Theory and 1,4-dihydroxy-3-amino-cyclohexa-2,5-dienyl radical has been determined as the most probable primary intermediate. (C) 2001 Elsevier Science B.V. All rights reserved.