The biogenesis of adrenal chromaffin vesicles will be investigated by studying the incorporation of H3-leucine into the soluble and membrane-bound proteins of the vesicles. H3-leucine will be injected directly into the adrenal glands of sheep and at various times afterward the subcellular distribution of soluble and membrane-bound radio-labeled proteins will be determined. Specific peptides and proteins will be identified by gel electrophoresis and immunoprecipitation. Analysis of the data will provide information on the incorporation of newly synthesized proteins into chromaffin vesicle membranes and to what extent "old" membranes are reutilized.