It is easy to make anecdotal claims for the efficacy of new forms of treatment based on the short term results in a small number of patients. Many authors have done this for endoscopic laser therapy in the gastrointestinal tract. It is very much more difficult to carry out a comprehensive assessment of the short and long term effects of new techniques and to compare these with the results of alternative treatments for the same diseases. This book, from one of the world's leading departments of gastroenterology, describes and analyses the largest series of patients yet reported from one centre treated endoscopically with the NdYAG laser for gastrointestinal disease. The follow up extends over 8 years and the results are impressive. Some of the early claims for laser therapy have been validated, others have not, but the real value of the book is that we now have a large amount of well organised data on which to judge the merits of laser therapy. Medical laser techniques are in their infancy and the potential for future develop- ment is enormous, but ideas on current applications have been consolidated and that is essential before the next concepts evolve. This book has taught us how to walk. The world is now ready to learn to run! S. G. Bown, Director National Medical Laser Centre London Contents INTRODUCTION 3 Introduction and purpose of the study 5 1 General aspects of laser 6 1. 1.