For the safe operation of living donor pancreas transplantation, we investigated the utility of 11C-methionine positron emission tomography (PET) to examine the function of the residual pancreatic head in patients with pancreatic disease undergoing distal pancreatectomy and in living donors of pancreas transplantation. After 6 hours of fasting, we intravenously injected 370 to 740 MBq 11C-methionine. PET was scanned 30 minutes after injection. 11C-methionine PET uptake by the pancreatic head versus body/tail was expressed as a standardized uptake value (SUV). The SUVs of the pancreatic head were compared before versus after surgery. The SUVs of the pancreatic head in patients before and after distal pancreatectomy were 15.3 +/- 6.0 and 18.2 +/- 2.4, respectively. The SUVs of the pancreatic head in donors before and after distal pancreatectomy were 16.1 +/- 1.0 and 14.7 +/- 1.4, respectively. Both patients and donors showed no significant difference in SUVs of the pancreatic head before and after surgery. However, the SUVs of the residual pancreatic head were elevated after distal pancreatectomy in 80% of patients and 50% of donors. These data indicated that the function of the pancreatic head may be maintained or improved after distal pancreatectomy. 11C-methionine PET may become a potent modality to evaluate segmental pancreatic function for a safe living donor operation.