Calcium dobesilate (Doxium) is used in the treatment of diabetic retinopathy. Clinical studies show a slowdown of the progression of the disease after long-term oral treatment. The main action of the drug is related to a reduction of microvascular permeability as measured by different parameters and methods (vitreous fluorophotometry, retinal haemorrhages, skin capillary resistance, blood albumin leakage, blood viscosity) leading to improved visual acuity. The pharmacological activity may be explained in part by the antioxidant properties of calcium dobesilate and its action on endothelium through the synthesis of nitric oxide, increasing the endothelium-dependent relaxation. The antioxidant effect was demonstrated in different in vitro and in vivo models by decreasing the peritoneal permeability in rats induced by pro-oxidant substances. Moreover, vascular leakage was also decreased by calcium dobesilate in a reperfusion model in streptozotocin induced diabetic rats after ischaemia of the central artery of the retina. Doxium may also preserve vascular endothelial function by acting directly as antioxidant to protect lipids from peroxidation.