Leukocyte adhesion was determined in diabetic rats after systemic treatment with L-NAME, a NO-synthase inhibitor. L-NAME significantly reduced leukocyte adhesion in the retinal arterioles (56%, n = 10, P < 0.0001), venules (68%, n = 10, P < 0.0001), and capillaries (52%, n = 10, P < 0.0001) when compared to nontreated diabetic animals. The treatment of nondiabetic animals with L-NAME also reduced leukostasis when compared to untreated nondiabetic animals.