[en] Vasopressin and oxytocin are stored within the neurosecretory granules of the posterior pituitary. The hormones are non-covalently bound to specific neurophysins, which are high molecular weight carriers. The major results obtained by the radioimmunoassay of neurophysins in the human and in animals are reviewed. The technique is highly reproducible, specific and sensitive. It has been used for the study of neurohypophysial function in physiological and pathological conditions. The method is more convenient than that for the assay of oxytocin and antidiuretic hormone. It is emphasized that the neurophysins do not themselves share any diuretic or oxytocic properties. The biological meaning of the results obtained should be interpreted with caution. (U.K.)