This is a specialized therapeutic procedure which involves evaluation of the bile ducts, pancreatic ducts, and gall bladder and subsequent treatment. Similar to an upper endscopy, a flexible tube is passed through the mouth and guided down to the top part of the small intestine. Once the duodenal papilla (the opening to the bile ducts) is located, a small catheter is passed through and dye is injected into the pancreatic or biliary ducts. X rays are then taken which help outline the anatomy and locate any blockages, malignancy, or stones. During an ERCP the endoscopist may remove any obstructions or place a stent that will allow for appropriate drainage of the ducts.
More information: http://www.asge.org/patients/patients.aspx?id=386