The monograph presents materials of experimental and clinical studies devoted to the study of the effect of both external radiation sources and incorporated radionuclides on the structural and functional state of the pancreas, the body's sensitivity to insulin and insulin-receptor interaction in cells, epidemiology, course and treatment of diabetes mellitus. Methods have been developed that can be used in medical practice to control the production of insulin preparations in pharmacological production and to isolate pancreatic islets for transplantation into patients with diabetes mellitus.