To the Editor.
—Mammalian cardiac atria contain biologically active peptides that are capable of producing diuresis, natriuresis, and vasodilation.1,2 Recently, we have shown that plasma levels of atrial natriuretic polypeptide (ANP) is significantly higher in spontaneously hypertensive rats at 20 weeks of age (blood pressure, 184 ±7 mm Hg) than values observed in age-matched normotensive Kyoto-Wistar strain rats3 (blood pressure, 114 ±5 mm Hg).A recently developed radioimmunoassay4 has permitted us to measureplasma ANP concentration in two patients with severe essential hypertension. The plasma ANP values were measured before therapy and after two weeks and four weeks of antihypertensive therapy with nifedipine.Report of Cases.—Case 1.—A 60-year-old man was admitted to our hospital as a hypertensive emergency, with visual disturbance. His pulse rate was 84 beats per minute and his blood pressure was 262/150 mm Hg. Severe hypertensive retinopathy, including massive retinal hemorrhage, was observed. Renal