The effect of calcium dobesilate on the alteration of the blood-retinal barrier was studied in 41 adult-onset, non-insulin dependent diabetic patients with minimal or no retinopathy, randomly assigned to receive either oral calcium dobesilate (1000 mg twice daily) or a placebo for 12 months. The posterior vitreous value and the penetration ratio, determined by vitreous fluorophotometry, reflected stabilisation of blood-retinal barrier permeability in the calcium dobesilate patients and deterioration of blood retinal barrier in those given placebo. During the relatively short period of the study, one year, no significant change in microaneurysm and capillary closure gradings was observed. No side effects were associated with calcium dobesilate.