This book originates from a symposium held at the London Hospital Medical College under the auspices of Applied Chromatography Systems Ltd. to discuss the place of HPLC in the endocrinology field. Many of the authors of the present book were speakers at this symposium. It seemed to us that many endocrinolo gists did not at that time fully appreciate the value of HPLC, and this book was designed to publicise the potential value of this technique. A survey of methods used in the steroid field Cp 185) confirmed the view that HPLC is not being used as widely, particularly in research described in clinical journals, as might be expected. We hope that this book will illustrate, albeit in a few selected areas of endocrinology, just how versatile and powerful a technique HPLC is, and en courage those who have not yet experienced it to have a go. The beginner does not need to buy expensive instrumentation - all that is required is a pump, injector, column and detector - the rest can come later! All the authors have practical experience in the use of HPLC in the particular area they discuss. All readers who discover apparent errors or who feel that the treatment of a topic of interest can be improved upon are encouraged to contact the editors. All criti cism, especially if constructive, is welcomed. We are still learning, and other peoples' experience is always valuable.