In this review the most recent advances in blood coagulation and chronic complications of diabetes mellitus are discussed. Numerous research workers have reported abnormalities in the mechanisms of platelet activation, endothelial cell function, plasma coagulation and fibrinolysis. However, the data available today cannot as yet be interpreted in terms of pathogenesis of retinopathy or any other chronic manifestation of the disease. Consequently, there is at present no rationale for pharmacological prevention or treatment.