An endoscope, a flexible fiberoptic scope with a light, is inserted through the mouth into the duodenum. A catheter is advanced through the endoscope and inserted into the pancreatic or biliary ducts. A contrast agent is injected into these ducts and X-rays are taken to evaluate their caliber, length and course. Endoscopic retrograde cholangiopancreatography (ERCP) is performed to identify any narrowing, stones, or tumors in the pancreatic or biliary ducts.Update Date: 3/8/2008 Updated by: Christian Stone, MD, Division of Gastroenterology, Washington University in St. Louis School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.