The structural analyses of the vasopressin and oxytocin prohormones have been completed. Post-translational conversion of the prohormones to peptide products has been localized to the neurosecretory granules (NSG). A new immunocytochemical method for the analysis of peptide localization at the electron-microscope level has been developed. Based on this method we have found that the AVP-containing NSG appears to also contain dynorphin 1-8. Voltage-sensitive dyes have been successfully used to record action potentials by optical methods in the posterior pituitary. Excessive exposure of neonatal rats to vasopressin produces a permanent type of nephrogenic diabetes insipidus in the adult rat. A tissue culture model which allows for the study of the development of AVP-receptors has been produced.