Interstitial and microvascular disorders are known as a characteristic part of the diabetic cardiomyopathy and to resist partly insulin therapy. Aim of this study was to demonstrate structure-protecting effects of Ginkgo Extract EGb 761 known as a natural radical scavenger in streptozotocin-diabetic rats on the microvascular compartment. Wistar rats (n = 5) were made diabetical by i.p. injection of 60 mg/kg body mass streptozotocin for 4 months. Rats of the protected group (n = 5) received daily 100 mg/kg body mass EGb 761 for 3 months, starting 1 month after induction of diabetes. 5 age-matched rats served as control. The volume fraction of interstitium was slightly but significantly increased only in the unprotected diabetic group. Diminishing of the capillary to the myocyte ratio was seen in the diabetic but not in the protected group. Immunostaining of collagen revealed a slight increase of type III, type IV, and type VI fibres in the interstitium, more expressed in the unprotected group. Ultrastuctural morphometry revealed significant thickening of endothelial and muscular basement membranes in diabetic animals, less expressed in the EGb- protected group. The capillary diameter was slightly increased in the diabetic and slightly decreased in the protected group. The number of plasmalemmal vesicles was tendentially more decreased, that of lysosomes more increased in the diabetic than in the protected group. It is concluded that EGb 761 can diminish partly interstitial fibrosis and reduce endothelial and muscular basement membrane thickening of the diabetic myocardium. It may contribute to prevent late diabetic complications.