Since the awarding of the Nobel Prize to Drs. Guillemin and Schally iJ) 1971 for isolation and chemical characterization of gonadotropin releasing hormone, we have experienced a remarkable period of growth of interest in this hormone. The last 20 years have been characterized by a swift translation of basic science discovery into clinical utility. Approval of GnRH and its analogs for treatment of prostate cancer, endometriosis, of ovulation indicate the range and precocious puberty and for induction of these agents. of usefulness In order to bring together the leaders in the basic and clinical science of GnRH, a conference was organized on Modes of Action of GnRH and GnRH Analogs and held in Scottsdale, Arizona, February 26 to March 2, 1991. The presentations, given as chapters in this volume, show both the advances in the body of information in this discipline and the efforts underway to reduce basic science to clinical practice. The audience was a combination of representatives from universities, government, industry, and physicians in practice. The lively discussions and insightful questions indicated the interest in the topics discussed and frequently served to catalyze planned interactions of the meeting participants. The organizers are grateful to the speakers and poster presenters for their contributions and for the timely preparations of the manuscripts included in the present volume. We are also thankful to the staff of Serono Symposia, USA, for the organizational skills and support that allowed the meeting organizers to focus on the science and medicine presented.