Daily pancreatic flow and daily outputs of bicarbonate and amylase in pure pancreatic juice were observed in 15 postoperative patients who underwent upper abdominal surgery. Exocrine pancreatic secretion under the stimulation by enodgenous or exogenous hormones was well correlated with the extent of pancreatic fibrosis estimated by the histometrical treatment. Exocrine pancreatic secretion in Billroth II type of gastrectomy was depressed to 60-70% of the patients' with Billroth I type of gastrectomy. In distal pancreatectomy the depression in the exocrine pancreatic secretion almost corresponded with the resected volume of pancreas. Exocrine pancreatic secretion in pancreatodoudenectomy was highly depressed beyond the expected value from the resected volume and fibrosis of the pancreas. This was interpreted as partly due to the elimination of hormonal mechanism by duodenectomy and partly due to the denervation of the secretory fibers by surgical manipulation.