SUMMARY: Renal excretion in intact, sham-operated and neurohypophysectomized ducks was studied. Neurohypophysectomy produced immediate and profound polydipsia and polyuria. These conditions steadily diminished during the first 2 weeks after the operation and by the 14th day they had stabilized at levels which were approximately three times higher than the corresponding values in sham-operated birds. The stabilized levels of polydipsia and polyuria persisted throughout the remainder of the 60–90 day experimental period. The rates of excretion of Na+, Cl− and total osmotically active material were also increased when compared with intact or sham-operated birds. No change in the rate of K+ excretion was observed. The i.m. administration of vasopressin reduced the rate of urine flow to that observed in the control birds but the rates of electrolyte excretion were not restored to normal. Synthetic oxytocin had no antidiuretic effect in the neurohypophysectomized birds. Arginine vasotocin treatment restored the rates of both water and ion excretion to values very close to those observed in intact and sham-operated birds.