Uninephrectomized adult female dogs with chronic indwelling catheters were maintained on a low sodium diet and studied without anesthesia. Following hydration with 3% dextrose, an intravenous infusion of either arginine vasopressin (AVP) or of 1-desamino-8-D-arginine vasopressin (DDAVP) was begun. The dose was calculated to achieve a near maximal physiological plasma concentration of AVP, or an equimolar concentration of DDAVP. Both AVP and DDAVP increased urinary osmolality from less than 60 to over 800 mosmol/kg H2O within 1 h. AVP infusion increased mean arterial pressure and renal electrolyte excretion and decreased heart rate and plasma renin activity (PRA), while DDAVP was without effect on these parameters. AVP infused into the renal artery at doses which did not alter systemic pressure and heart rate caused kaliuresis and reduced PRA. We conclude that the AVP-induced inhibition of renin secretion and increase in renal electrolyte excretion are not secondary to increased tubular permeability to water, but must represent a more specific action of AVP which is not shared by DDAVP.