In this paper, ZnO nanoparticles have been synthesized with and without the use of surfactants under different reaction conditions. The size of the ZnO nanoparticles varied in diameter (2 nm-28 nm) according to the reaction conditions employed. Promising particle size dependent antibacterial and antifungal activities of the ZnO nanoparticles have been observed. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Infrared spectroscopy (FTIR) techniques were used to characterize the particle size and morphology. (C) 2010 Elsevier B.V. All rights reserved.