The objective of the research proposed here is to combine four projects into a unified program of research for which the central theme is a study of the hormone human choriogonadotropin (hCG). The component projects are (1) protein chemical studies of hCG, (2) immunochemical studies of hCG, (3) studies related to the tertiary structure of hCG, and (4) clinical applications of hCG detection. The objectives of the program, in addition to those implied by the titles of the projects, are to study determinants on the surface of hCG responsible for biological and immunological recognition of the hormone, to establish a wide variety of antibody producing mouse myeloma hybridoma cell lines prepared against different components of the hCG molecule or its receptor, to study the comparative structure of primate gonadotropins, to express the cloned genetic information for the alpha and beta subunits of hCG in bacteria in an effort to prepare their polypeptide chains free of carbohydrate for use in x-ray crystallograph studies, to identify the nature of the molecule in pregnancy urine responsible for immunosuppressive activity, to improve methods for the detection of hCG and to apply these in clinical studies, and to establish a well-characterized library of hCG reagents for the purposes of studying the relationship of structure to function.