Pancreatic endocrine function was investigated in dogs after heterotopic pancreatic allotransplantation. A marked hyperinsulinemia was found in peripheral venous blood within the first 60 min postoperatively. This was associated with hypoglycemia and hypokalemia occurring within the next 2 to 3 hr resulting eventually in death. The hypoglycemia and hypokalemia could be corrected by parenteral dextrose and potassium given during the first 2 hr postoperatively or prevented by parenteral hydrocortisone given at the time of transplantation.