Endocrinology and Metabolism: Progress in Research and Clinical Prac­ tice is a new series that has been designed to present timely, critical reviews of constantly evolving fields; to provide practical and up-to-date guidance in the solution of pertinent clinical problems; to offer an alterna­ tive to the laborious search of the literature (and the often frustrating reading of highly technical articles); and to translate the language of the laboratory into that of the practice of medicine. We think that this volume and those to come will prove useful to physi­ cians (and to physicians in training), as well as to investigators in a wide variety of specialties; in short, to anyone who seeks answers to questions in endocrinology and metabolism. The first chapter of this volume could well serve as a general introduc­ tion to the entire series. It points out how our growing understanding of the molecular basis of biologic communication has led to the discovery of a growing number of clinical syndromes, as well as to the realization that phenotypically similar diseases may have radically different pathogenetic mechanisms and thus may require radically different therapeutic strata­ gems.