50 patients with diabetes mellitus of 2-7 years' duration were divided by a random method into 2 equal groups, one of which received 1,500 mg of Doxium (calcium dobesilate) daily for 3 months, the other group receiving a placebo. All the patients had diabetic retinopathy, open-angle glaucoma, raised intraocular pressure, and hyperviscosity of whole blood, plasma, and aqueous humor. 10 patients in each group underwent operation for glaucoma. At the end of the trial the state of the retina, the visual acuity, and the visual fields had improved, and the intraocular pressure and the 3 viscosity values had fallen to a statistically significant extent in the Doxium group compared with the initial status and with the placebo group. These results are consistent with Doxium's known action in reducing capillary fragility, microvascular hyperpermeability, and blood viscosity.