A “blind” study on the ultrastructure of the dermal capillaries of Africans in Johannesburg, South Africa, is reported. None of the patients had a family history of diabetes mellitus, and all were normotensive. A group of African, nondiabetic, normotensive ward patients with normal glucose tolerance curves acted as controls. As a corollary, a small group of Indian (Asiatic) and white patients were included in the sample to determine if any capillary changes could be related to ethnic group, diet, or other circumstances. The results indicate that thickening of the basal lamina (basement membrane) in the dermal capillaries of Africans is not specific for diabetes mellitus, and that no significant ultrastructural differences exist among the diabetics of the three major ethnic groups. However, it appears that the capillary lesion is commoner in diabetics than in nondiabetics, and the role of the pericyte in the possible pathogenesis of the lesion is discussed.

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