A reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H)-dependent hydrogen peroxide-generating activity of rat ocular tissue was investigated cytochemically utilizing the cerium method. NADPH or NADH oxidation resulted in electron-dense fine granular deposits on the corneal epithelial and endothelial plasma membranes, around the photoreceptors of the retina, and on the processes of the retinal pigmented epithelium. Control specimens incubated in a substrate-free medium did not show any such deposits. These results suggest that, under normal conditions, there is generation of oxidants, such as hydrogen peroxide, in the ocular structures, and that such oxidants can be visualized by cytochemical techniques.