In a prospective clinical-experimental study, 15 consecutive patients with chronic pancreatitis, operated on because of severe pain, were examined for the effects of a duodenum-preserving resection of the pancreas head on endocrine pancreas function. This was done by means of oral and intravenous glucose tolerance testing before the operation, on the 10th or 11th day postoperatively, and 3 months after the operation. In addition to glucose levels in the peripheral venous blood, levels of insulin, C-peptide, glucagon, and pancreatic polypeptide were determined. As indicated by the k value, glucose tolerance improved postoperatively in 10 patients (66.6%); three patients (19.9%) showed no change, and one patient (6.6%) was worse. Only one patient (6.6%) developed evident diabetes mellitus immediately postoperatively. Pre- and postoperative levels of insulin and C-peptide showed no significant differences. The fasting levels of glucagon were significantly lower postoperatively than before the operation (p < 0.01). The stimulation of pancreatic polypeptide after oral glucose was significantly lower postoperatively (p < 0.01). Duodenum-preserving pancreas head resection does not lead to an impairment of glucose tolerance in the majority of patients; a deterioration was observed only in few cases (13.3%).