The Fifteenth Midwest Conference on Endocrinology and Metabolism, held at the University of Missouri-Columbia on October 11 and 12th, 1979, hosted the most prominent active researchers in the world on the subject of the hormone relaxin. Each speaker presented an in-depth coverage of his chosen topic and area of expertise. Some of the data presented in this book are findings which have not been pub­ lished in a scientific journal. The topic of this conference is especially timely in light of the fact that this is a first confer­ ence devoted specifically to the hormone relaxin. Progress on this hormone has been exceedingly rapid in recent years and many signif­ icant breakthroughs are documented in these pages. Lively discus­ sions following each presentation attest to the enthusiastic research effort being pursued at the present time concerning relaxin. Traditionally the Midwest Conferences on Endocrinology and Metabolism have emphasized breadth as well as depth of coverage. The present Conference has covered the many active areas of research in relaxin, including morphological aspects of the hormone's origin, chemical purification and chemical structure, bioassays, radioimmuno­ assays, receptors, mechanism of biochemical action and physiological responses to the hormone. Advances in relaxin were slow since its discovery by Dr. Frederick Hisaw, Sr. in 1926 until the availability of homogenous preparations some seven years ago. In the suceeding seven years, activity in the subject has accelerated remarkably.