Abstract Mean fasting preoperative pancreatic polypeptide levels in a group of 18 patients with duodenal ulcer disease were 462 ± 88 pg/ml, with 13 patients having markedly elevated levels (mean 600 ± 106 pg/ml) and 5 patients having normal or minimally elevated levels (mean 112 ± 32 pg/ml). Mean fasting postoperative pancreatic polypeptide levels significantly decreased to 136 ± 36 pg/ml, with decreases occurring in 12 of 13 patients who had had markedly elevated preoperative values. Parietal cell vagotomy and truncal vagotomy produced significant reductions in both fasting pancreatic polypeptide levels and in the glucose-stimulated pancreatic polypeptide response during the first 60 minutes. There was no correlation between pancreatic polypeptide levels (fasting and stimulated) and duration of ulcer disease, indications for ulcer operation, type of operation, or age of patient. These results suggest that elevated fasting pancreatic polypeptide levels may indicate vagal hyperactivity in some patients with duodenal ulcer.