Pancreatic polypeptide (PP) is a 36-amino-acid secretory peptide that is predominantly produced by the pancreas. The exact physiologic role of PP in healthy individuals has not been fully defined. It has been shown, however, that pancreatic polypeptide affects the secretion of pancreatic enzymes, water, and electrolytes. Its effect is biphasic in that PP initially enhances secretion and then inhibits secretion. PP increases gastric emptying and gut motility. Pancreatic polypeptide also relaxes the pyloric and ileocecocolic sphincters, the colon, and gallbladder. PP levels increase after ingestion of food and remain elevated from four to eight hours. Prolonged fasting, diabetes, and exercise can also increase PP levels. Serum PP levels can be elevated in as many as 50% of patients with carcinoid syndrome. Increased levels can also be found in patients with duodenal ulcers and in patients with type I diabetes. PP levels are often low in patients with pancreatic insufficiency or pancreatitis.