Bovine pancreatic peptide (BPP) is a straight chain peptide containing 36 amino acid residues that has recently been isolated from pancreatic tissue. At a dose of 40 mug/kg-h intravenously, it stimulated gastric acid secretion when given alone but inhibited the submaximal secretion induced by the C-terminal pentapeptide of gastrin. Basal pancreatic secretion of dogs was inhibited by BPP (1-10 mug/kg-h) inhibited pancreatic protein secretion but often showed a biphasic action on water-bicarbonate response, an initial augmentation followed by reduction. BPP (2-5 mug/kg-h) inhibited pancreatic water-bicarbonate and protein secretions induced by an infusion of secretin plus cholecystokinin. Des-tyrosyl-NH2 BPP lacking the C-terminal tyrosyl amide, failed to inhibit gastric acid induced by C-terminal pentapeptide of gastrin or pancreatic secretion induced by secretin. BPP had no hyper- or hypoglycemic, hyperkalemic, or diuretic actions in the dog.