Backing up the pioneering medical researchers and experi menters are the phalanxes and cohorts of practising clinicians in district general hospitals and in general practice who may have to implement and apply any breakthroughs and advances in practical and realistic terms. This they cannot, and should not, be expected to do without careful consideration and analysis. It is essential, therefore, to have regular reviews of the growing points of medicine which are constructively critical as well as being enthusiastic and which can present the issues and implications clearly and fairly to clinicians. The Practical Clinical Medicine series is designed to provide such regular reviews on selected subjects. Each volume is under the charge of an invited editor who selects his team of 4-6 experts. Each contribution is an authoritative, detailed and referenced examination of his topic, is clearly presented in an understandable manner and is practical, relevant and applic able to everyday clinical practice. The series is intended as a means of communication between researchers and practising clinicians. It is dedicated to gener alists who provide primary health care in general practice and to generalists providing secondary medical care in district vii viii Series Editors' Foreword general hospitals. Both are involved in applying good general practical clinical medicine for their patients, but can only succeed in a climate of constant review and examination.