Various types of insulin- and glucagon-containing endocrine cell distribution were found by double staining with antibodies to insulin and glucagon in the pancreatic autopsy material from subjects without carbohydrate metabolism disorders. The cell composition of the islets and their morphogenetic maturity depended on the vascularization degree. Insulin-containing cells predominated in small clusters of endocrine cells and in islets with few capillaries, while glucagon predominated in large islets with rich vascularization. A scheme of development and differentiation of Langerhans islets in the adult human pancreas was presented.