application of vasopressin radioimmunoassay to clinical study role of vasopressin in hypo and hypernatremia and some other disorders of water metabolism plasma and urinary arginine vasopressin avp in normal subjects and in patients with various water metabolism disorders was measured using a sensitive specific radioimmunoassay the avp plasma levels in normal subjects were 31 12 pgml the parallel changes in plasma osmolality plasma avp concentration and urinary osmolality were observed after water load in patients with various kinds of hyponatremia and impaired water excretion plasma avp concentrations were within or over normal levels suggesting that persistent secretion of avp may play an important role in the pathogenesis of hyponatremia variable levels of plasma avp were observed in patients with essential hypernatremia which in turn suggested that osmoreceptors may be selectively damaged in some patients and that adhsecreting neurons are also involved in others our radioimmunoassay facility made it possible for us to measure plasma and urinary ddavp in the treatment of diabetes insipidus