We investigated antibacterial activity of ZnO nanorods prepared by a hydrothermal method against a gram-negative bacterium Escherichia coli and a gram-positive bacterium Bacillus atrophaeus. Antibacterial activity of ZnO nanorod coatings was studied on solid substrates covered with nutrient agar, as well as in liquid nutrient broth for different concentrations of ZnO nanorods, nanoparticles, and powder. ZnO exhibited antibacterial activity against both E. coli and B. atrophaeus, but it was considerably more effective in the latter case (at 15 mM vs. 5 mM concentration, respectively, showing zero viable cell count). For both organisms, damage of the cell membranes was found, and the effect was more pronounced for B. atraphaeus. Chemiluminescence analysis has been used to detect the release of hydrogen peroxide from ZnO structures, and the effect of H(2)O(2) on the E. coli and B. atrophaeus was studied. Since significant differences were observed in the effect of ZnO nanostructures and H(2)O(2) on B. atrophaeus, it can be concluded that there are other mechanisms contributing to the antibacterial activity of ZnO nanostructures. (C) 2007 Elsevier B.V. All rights reserved.