1. The hypotensive effect of spironolactone has been studied in twenty-four patients with various forms of hypertension.
2. In essential hypertension a greater fall of blood pressure was achieved in patients with renin activity hyporesponsive to postural change than in those in whom renin responded normally to posture.
3. A poor hypotensive response was observed in patients with renal or renal arterial disease and secondary aldosteronism.
4. The variable hypotensive response seen in patients with primary aldosteronism predicted the response to adrenal surgery.
5. Blood pressure was not lowered by spironolactone in one case of 17-hydroxylation deficiency or in one case of malignant ovarian arrhenoblastoma producing aldosterone.