The successful use of nanoparticulate ZnO in applications such as UV-screening agents or photocatalyst for the destruction of chemical waste requires the development of techniques for controlling its photocatalytic activity. In this study, we have investigated transition metal doping as a means of achieving this goal. Powders of ZnC, MnxZn1-xO. and CoxZn1-xO were synthesised by a three-stage process consisting of high-energy mechanical milling, heat treatment, and washing. The photocatalytic activity of these powders was evaluated using the spin-trapping technique with electron paramagnetic resonance spectroscopy. It was found that the photocatalytic activity of CoxZn1-xO progressively decreased with the doping level. In contrast, the activity of MnxZn1-xO initially increased with doping up to a level of 2 mol% and thereafter declined. These results demonstrate that doping with transition metal oxides can be used to tailor the photocataiytic properties of nanoparticulate ZnO. (c) 2008 Elsevier B.V. All rights reserved.