The impact of small differences in selenium exposure during the first year of life was investigated in male Wistar rats. Forty-five rats were evaluated in two experiments. Rats were provided diets that contained sucrose as the sole carbohydrate to induce an elevation in blood triglycerides, cholesterol, glucose, and insulin. In each experiment one-half the rats received 0.1 mg Se/kg and the other half 0.2 mg Se/kg diet. Both levels of selenium supported normal activity of the marker for selenium sufficiency erythrocyte glutathione peroxidase. In experiment 1 rats were maintained in galvanized cages and in experiment 2 they were housed in stainless steel cages. In both experiments rats provided 0.2 mg Se/kg diet had fewer acellular degenerating capillaries and a higher ratio of pericyte to endothelial cells in the capillary wall than those fed 0.1 mg/kg as well as fewer vessels over the optic disc head. In the second experiment, the height of the central choroid was also greater in rats exposed to the higher level of selenium suggesting that the element protected the capillaries in this region from degeneration. In contrast to vascular tissue, the retinal parenchymal tissue was unaffected by the level of selenium exposure. These results are consistent with the hypothesis that the microvasculature has a unique requirement for selenium.