The editors have asked me to write this foreword probably for two reasons: First, I have spent 35 years trying to develop radiolabeled compounds that would help diagnose and treat disease. I, and the people from my laboratory, have been much involved with developing Nan'I for the diagnosis and treatment of hyperthyroidism and well-differentiated thyroid cancer. Second, I was a participant throughout the entire symposium upon which this book is based. Our latest '311-labeled compound, [l3lll metaiodobenzylguanidine, took us 13 years to develop. It has succeeded in diagnosing and treating adrenergic tumors '31 under circumstances where Na 1 would have failed for the diagnosis and treatment of thyroid cancer. I therefore hope that more scientists will be attracted to this field. This book is written by intelligent, experienced investigators who are knowl­ edgeable. It is a must for anyone new in the field. For the experienced, I would like to remind you that I attended the entire symposium; the breadth and timeliness of the update has helped us to redirect some of our current efforts into more scientifically productive channels. William H. Beierwaltes, M.D.