The effects of 2 potassium‐retaining diuretics on arterial pressure, intravascular volume, responses of the renin‐angiotensin‐aldosterone system, serum electrolytes, and renal function were compared by means of an 8‐wk double‐blind, crossover trial in 13 patients with “volume‐dependent” essential hypertension. The fall in systolic, diastolic, and mean arterial pressures in the supine and erect positions (all p<0.005) induced by spironolactone was greater than that by triamterene. The pressure fall induced by spironolactone was also associated with a persistent contraction in plasma volume (p<0.05) and a secondary hyperaldosteronism that was not accompanied by hypokalemic alkalosis. The pressure fall induced by triamterene was not associated with reduced plasma volume, effect on plasma renin activity, or aldosterone excretion. Both drugs produced significant rises in blood urea nitrogen and creatinine levels that never exceeded normal limits.Clinical Pharmacology and Therapeutics(1980)27,53–56; doi:1