The object of this preliminary study was to evaluate the endocrine function after heterotopic intraperitoneal segmental pancreatic allotransplantation with unligated duct in irradiated, totally pancreatectomized primates. All allograft recipients received, pre- and peroperative donor-specific blood transfusions and peroperative external irradiation from a linear accelerator; 200 rads was administered weekly and increased to a total dose of 1,500 rads. Pancreatic transplantation was performed between 2 and 6 weeks after completion of irradiation and preoperative blood transfusions. As previously reported, only minimal pancreatic allograft survival was achieved following preoperative irradiation. One recipient remained normoglycaemic for greater than 100 days after transplantation, the longest surviving pancreatic allograft recipient reported from this laboratory. Intravenous glucose tolerance test results in this recipient revealed normoglycaemia, reduced K-value, hypoinsulinaemia, normal glucagon response, reduced C-peptide values, and moderate glucose intolerance. Aortography and electron-microscopic examination of allograft biopsy tissue confirmed the presence of a functioning allograft.