The endoscopic use of lasers in the treatment of gastrointestinal d~seases began within the last decade and has evolved rapidly. Work is now being done at more than 150 centers in Europe, the United States, Japan and the rest of the world. To date no publi cation has defined the state of the art. This text attempts to fill that void. To disseminate information about therapeutic laser endoscopy, an increasing number of short courses have been sponsored in the United States wherein the attendee hears didactic lectures, views video tapes, and in addition, has the opportunity to have a "hands-on" experience with endoscopic laser therapy in the animal labs. This book is an expansion of the material presented in one such course sponsored by The Cook County Hospital in Chicago, Illinois, in October, 1982. The course was organized by Peter Bright-Asare, M. D. , Chairman of Gastroenterology at the time of the course and chaired by Dr. Bright-Asare and myself. Some of the lectures from the course have been broadened and formalized. Other chapters were invited and added. Also included are group discussions about issues that are either controversial or undefined. Attempts were made to secure consensus opinion from experienced investigators in areas where no hard scientific experimental or clinical data exists. The contributors have a wide range of interest and expertise. Dr.