The effects of prostaglandin E1 on fluid and sodium excretion, creatinine clearance and renin release were examined in 26 hypertensive patients including 9 cases of essential hypertension, 10 of renovascular hypertension and 7 of primary aldosteronism. When prostaglandin was infused intravenously in a total dose of 120μg in 60min, urine volume was increased in 70% of cases, and sodium excretion in 61%, but little changes were observed in creatinine clearance. The most prominent diuresis and natriuresis were obtained in primary aldosteronism (mean increase was 319% in urinary volume, and 222% in sodium output). The average increases in urinary volume were 61% in patients with essential hypertension and 97% in renovascular hypertension. And urinary output of sodium was increased by 63% in the former and 56% in the latter. The remarkable renal effects of prostaglandin El in primary aldosteronism were completely abolished after the administration of spironolactone. Significant elevation of plasma renin activity resulted from prostaglandin El infusion in essential hypertension, while no constant effect was obtained in renovascular hypertension and primary aldosteronism. The present experiments indicate that prostaglandin El has different effects on the kidney according to the types of hypertension and the effects correlate closely with patient's status of extracellular fluid volume or sodium balance.