In 6 diabetic rats about 1,000 isolated islets of Langerhans were transplanted into the liver with little effect on the uninsulinism and hyperglycemia. Subsequently, a second transplantation resulted in a decrease of blood sugar to normal and in a reversal of the loss in body weight. Finally, in animals who had reversed to diabetes again, a third islet transplantation was performed. These rats with a total of 3,100 islets showed a decrease in the glucose levels from 250–305 to 110 ± 27 (X + SEM) mg/l00 ml. The insulin level after glucose stimulations was measured at 27 < X < 35 µU/ml.