When they were discovered by Acher and co-workers, neurophysins were thought to act as carriers for the active nonapeptides vasopressin (AVP) and oxytocin (OT) and were then recognized as the inactive fragment of a precursor with a higher molecular weight (propressophysin). The role of neurophysins in the hypothalamo-neurohypophyseal system is now being reconsidered in the light of crystallographic and molecular biology research and the recent definition of the different deletions or substitutions that cause central diabetes insipidus in rats (Brattleboro) or human beings. Apparently, any disruption of the structure and/or conformation of neurophysins (by genic substitution or deletion) may cause a decline in the binding and the activity of the endopeptidase responsible for the cleavage of the AVP. The disruption may also produce a change in the polymerization of neurophysins and salt bridges relating this to the neuropeptides, with the result that there is an accelerated aspecific enzymatic degradation of the hormone revealing clinical symptomatology. So, rather than being a mere inactive part of the precursor, neurophysins are now equally regarded as a system for carrying and protecting nonapeptides.