The effects of major abdominal surgery and nutritional support upon pancreatic function and morphology were studied in similar groups of patients who underwent major abdominal surgery (n = 18), received parenteral nutritional support (n = 18) or received enteral nutritional support (n = 16). The exocrine function of the pancreas was measured by means of an oral pancreatic function test (using 1 g of N-benzoyl-L-tyrosyl para-aminobenzoic acid) with measurement of serum para-aminobenzoic acid at 3 h and the Pancreatic Excretion Index. Pancreatic morphology was assessed by real time ultrasound and a pancreatic size index was calculated (maximum diameter of head x body). Serial measurements of function and morphology were carried out in each patient at entry into the study and at 7 and 14 days after operation or start of nutritional support. Serum PABA levels were similar in the 3 groups at the start of the study. Although the levels remained unchanged in the enteral and parenteral groups, a significant and progressive decrease was observed in the surgical group (serum PABA = 27.5 nmol/l (24.0-30.6) before operation, 10.5 nmol/l (5.5-13.4) 14 days after operation, P < 0.01). No significant changes in pancreatic size were seen. Parenteral and enteral nutrition preserves pancreatic exocrine function. A dramatic reduction in pancreatic exocrine function is seen after major abdominal surgery.