Conjunctival biomicroscopy was applied to the study of microcirculation in 30 healthy persons and in 112 patients suffering from diabetes mellitus before and after the treatment. Marked darangement of the end blood flow was expressed in the appearance of perivascular, vascular, and intravascular lesions, increasing with the progress of diabetes mellitus. Adequate therapy gave positive results with the disappearance or reduction of perivascular lesions in the microcirculation, and also improvement of the rheological properties of the blood.