Vitreous fluorophotometry (VF) has been used to study the blood-retinal barrier in rats with streptozocin-induced diabetes. Subsequent investigations have shown that many variables other than diabetes influence VF values. With the use of a commercially available fluorophotometer, we assessed VF measurements in diabetic rats while simultaneously measuring other variables, including plasma fluorescein level, free plasma fluorescein level, and blood pH. Mean total plasma fluorescein concentration, mean free plasma fluorescein concentration, and mean midvitreous fluorescein concentration were significantly decreased in diabetic animals. The mean ratio of midvitreous fluorescein concentration to total plasma fluorescein concentration was significantly increased in diabetic animals. In comparison with nondiabetic animals, the diabetic animals showed no significant difference in blood pH or mean ratio of free plasma fluorescein concentration to total plasma fluorescein concentration. Our findings confirm an early derangement of the blood-retinal barrier in diabetic rats.