We have investigated the metabolic effects of segmental (neoprene-injected) pancreas transplantation versus whole (enteric-diverted) pancreas transplantation. Seventeen uremic insulin-dependent diabetes mellitus (IDDM) patients received a simultaneous pancreaticorenal transplant: in a prospective, randomized study, 9 patients received a segmental neoprene-injected graft (group A) while 8 patients received a total pancreaticoduodenal graft, with enteric diversion (group B). The immunosuppressive therapy was based on ALG, CsA, azathioprine, and steroids. Three months after surgery, patients were submitted to the following metabolic investigation: i.v. and oral glucose tolerance tests, Hba1, i.v. arginine test, and a 24-hr metabolic profile. The OGTT, HbA1, and metabolic profile were repeated 12 and 24 months after transplantation. At 3 months after transplantation, the OGTT showed delayed insulin secretion and higher blood glucose levels in group A. Serum insulin levels after IVGTT or arginine were higher in group B than in group A. OGTT at 12 and 24 months were unchanged in group B, while in group A a higher incidence of impaired glucose tolerance (IGT) and diabetes mellitus response were observed. HbA1 and blood glucose levels during the 24-hr profile showed good metabolic control in both groups at 3, 12, and 24 months. We can conclude that both the segmental and total pancreas transplantation restore a good metabolic control in IDDM patients, though a higher incidence of IGT and DM responses were observed after OGTT in the patients receiving a segmental graft. These abnormalities do not seem to interfere with metabolic control in everyday life. These results seem to be the consequence of the different B cell masses transplanted with these two techniques.