This study was undertaken to determine whether or not changes occur in blood vessels, axons or glia of the optic nerve as the result of streptozotocin-induced diabetes. Diabetes was induced in 4 weeks old Sprague-Dawley rats. At 12 and 16 weeks of age, the rats were killed and the optic nerves prepared for examination. The number and density of blood vessels was found to be significantly increased in the diabetic rats. No alteration in the structure of the blood vessels was noted. A decrease in the percentage volume of axons and an increase in the percentage volume of glial elements accompanied the increase in blood vessels in the diabetic rats. No difference was found in the spectrum of fibre diameters.