The feeding of starch- or sucrose-rich diets to normal rats for 20 days resulted in a significant increase in lactate level and L/P ratio in the retina in the sucrose-fed animals. There was no correlation between the glucose and lactate content of the blood and retina and it was concluded that the increased lactate content of the retina was derived from the fructose moiety of the sucrose. Liver hypertrophy occurred in both normal and diabetic animals fed the sucrose diet. When streptozotocin-diabetic rats were maintained for 20 days on the same diets significant increases in the lactic acid content of the blood and liver occurred, but the high level of lactate in the retina of the sucrose-fed normal rats was not further elevated. The feeding of sucrose to diabetic rats resulted in better metabolic control of both blood glucose and lactate as compared with the maintenance of these animals on a starch diet.