The following remarks are intended to serve as an introduction to this particular volume as well as to the whole series of volumes of which this is the first. The intent of the series is to provide an authentic and relatively complete statement about the status of our understanding of the receptors. The models we had in mind while developing this series are The Enzymes, The Proteins, and comparable groups of books. The receptors have received a degree of importance and richness of understanding that makes them deserving of comprehensive and complete coverage. The study of these molecules,...