The present findings of increased microvascular protein passage are compatible with the hypothesis that the organic, histologically demonstrated diabetic microangiopathy is a long-term effect of periods of increased extravasation of plasma proteins, with subsequent protein deposition in the microvascular wall, i.e., the concept of plasmatic vasculosis. Arterial hypertension, frequently present in diabetes, enhances the development of arteriolar hyalinosis. Effective treatment of diabetes and hypertension arrests development of the microvascular lesions.