In rats made hypertensive by partial constriction of one renal artery and contralateral nephrectomy, large doses of furosemide had no hypotensive effect. However, when furosemide natriuresis was followed by removal of the clamped kidney, arterial blood pressure was greatly reduced. The fall of blood pressure induced in this manner was significantly correlated with the amount of sodium and water lost. The absence of a hypotensive effect of furosemide in rats with one-kidney Goldblatt hypertension appeared to be due to enhanced renin secretion. Furosemide not followed by nephrectomy caused a fall of blood pressure in rats with one-kidney Goldblatt hypertension after renin-depletion by desoxycorticosterone and salt treatment. Sodium wastage induced by peritoneal dialysis after removing the clamped kidney also lowered the blood pressure of hypertensive rats.