A series of studies to elucidate the biogenesis of the catecholamine storage vesicles of the adrenal medulla are proposed. By measuring the incorporation of a radioactive amino acid into the soluble and membrane-bound proteins of the vesicles it will be determined whether pre-existing membrane structures are reutilized in the formation of the vesicles or whether the formation of new vesicles requires de novo synthesis of the protein components of the membrane. From the proposed experiments the extent of reutilization of membrane proteins, if any, and the extent of new membrane protein synthesis will be evaluated. Studies will also be carried out to determine the subcellular sites of formation of both the soluble and membrane-bound proteins and the manner in which they are assembled into the intact vesicle.