The effect of 1-deamino-8-D-arginine vasopressin (DDAVP) on mean arterial pressure, pulse rate (PR), plasma renin activity (PRA), plasma factor VIIIc and von Willebrand factor were studied in a case of persistent lithium-induced nephrogenic diabetes insipidus (LINDI). 20% decrease in MAP, 22% increase in PR, 100% in PRA, and release of coagulation factors (2- to 3-fold) were noticed after infusion of 0.3 micrograms/kg DDAVP. Urinary prostaglandin (PG) E2 were enhanced. The treatment of this LINDI by PG synthesis inhibitor (PSI) combined with a low osmotic diet (LOD) led to a 51% fall in urine volume, 57% in free water clearance and 75% in sodium clearance. Urinary osmolality rose by 42% but remained low, probably in part because of the LOD. Urinary PGE2 was about one fifth of the initial high value. The results argue for (1) an end-organ resistance to DDAVP confined to the kidneys in LINDI and (2) an effectiveness of indomethacin combined with an LOD.