Pancreastatin is a 49 amino acid peptide originally isolated from porcine pancreas on the basis of its C-terminal glycinamide as isolation criterion. It is derived by proteolytic processing from chromogranin A, an acidic protein component of secretory granules in endocrine and neuronal cells. The primary structures of human, porcine, bovine and rat pancreastatin have been determined on the protein or cDNA level and show 70% sequence homology. By immunocytochemistry, pancreastatin has been detected in the pituitary, adrenal gland, pancreas, CNS and throughout the gastrointestinal tract. In pancreatic islets, pancreastatin is co-localized with insulin, glucagon and somatostatin. The principle biological activities of this peptide are: inhibition of insulin release and of exocrine pancreatic secretion. These effects which can be assigned to the amidated C-terminal part of the molecule have been demonstrated in several species. Whether or not pancreastatin can be classified as a novel peptide hormone that under physiological conditions plays a role in the regulation of the endocrine and exocrine pancreas, is still a matter of controversy.