The effects on pancreatic secretion of a diet supplemented with wheat bran for one month were studied in five dogs provided with chronic pancreatic and gastric fistulae. Dogs were subjected before and after bran administration to a continuous intravenous infusion of secretin (GIH, 0.5 U/kg/h) alone and a combination of secretin with cerulein (25 or 100 ng/kg/h). Exocrine pancreatic secretions under basal conditions were collected during the intravenous infusions of normal saline. Wheat bran supplementation for 4 wk to the standard diet in dogs increased pancreatic juice flow rate along with bicarbonate and amylase output whether the secretion was unstimulated or stimulated with caerulein alone or combined with secretin. No significant changes in the concentration of pancreatic bicarbonate, amylase, chymotrypsin, and proteins were noted under stimulated conditions. Furthermore, lipase concentration and output were dramatically reduced. These data indicated that wheat bran supplemented to the standard diet in dogs affects the exocrine pancreatic secretion whether it was unstimulated or stimulated by secretin alone or combined with cerulein.