Exocrine and endocrine functions of the pancreas were assessed in 44 Japanese patients who underwent pancreatic head resection. Functions were analyzed comparing levels before surgery, at a short-term follow-up (<2 months), and at a long-term follow-up (12-31 months). The N-benzoyl-L-tyrosyl-p-aminobenzoic acid (BT-PABA) excretion test, fasting blood sugar (FBS) level, and oral glucose tolerance test (OGTT) were used to determine pancreatic function. The patients were divided into three groups according to the size of the main pancreatic duct: group 1, 15 patients with a normal sized duct (< or =3 mm); group 2, 20 with a moderately dilated duct (>3 mm, <10 mm); and group 3, 9 with a markedly dilated duct (> or =10 mm). The mean BT-PABA value (6-hr urinary PABA recovery rate) in group 1 showed no change during the postoperative period. In contrast, the BT-PABA values in groups 2 and 3 had dropped by the short-term follow-up and returned to the preoperative level by the long-term examination. FBS and 120-min OGTT levels were not different between the three groups preoperatively. Although these values showed no change in all the three groups at the short-term measurements, the FBS in group 3 and 120-min levels in all the three groups had increased at the long-term. These findings suggest that exocrine pancreatic function shows a short-term deterioration in patients with a dilated pancreatic duct but recovers to the preoperative level over the long term after pancreatic head resection. Endocrine insufficiency, however, may occur at a long-term point after surgery irrespective of the preoperative pancreatic ductal dilatation.