We examined the chronic effects of losartan (DuP 753), a novel orally active angiotensin II receptor antagonist, on blood pressure and renal function in eight hospitalized patients with essential hypertension. After a control period of 1 week, losartan was administered orally once a day for 2 to 4 weeks in increasing doses of 12.5, 25, 50, and 100 mg, until blood pressure in the supine position decreased more than 20 mm Hg (systolic) and 10 mm Hg (diastolic) (or 13 mm Hg in mean blood pressure). The average dose of losartan was 59.4 +/- 43.7 (mean +/- SD) mg/day. Systolic, diastolic, and mean blood pressures, according to 24 h monitoring, fell significantly, from 151.9 +/- 6.8 to 137.2 +/- 7.9 mm Hg, from 90.6 +/- 3.7 to 81.0 +/- 3.7 mm Hg, and from 111.1 +/- 4.6 to 99.7 +/- 5.0 mm Hg, respectively (mean +/- SE, P < .01 for each), with no change in circadian rhythm or variability of blood pressure. Reduction in blood pressure was slightly greater during daytime than during sleep time. Unlike peptide angiotensin II antagonists, losartan did not exert pressor action. No significant alterations were observed in body weight, serum electrolytes, creatinine clearance, urine volume, or urinary excretion of sodium. Losartan significantly lowered serum uric acid concentration from 5.5 +/- 0.4 to 4.8 +/- 0.3 mg/dL (P < .05). Urinary excretion of uric acid increased significantly from 498.9 +/- 64.4 to 540.6 +/- 66.6 mg/day (P < .05). Plasma renin activity rose significantly but plasma aldosterone concentration did not change with the losartan treatment. These results suggest that losartan has a long-acting hypotensive effect with a hypouricemic action in essential hypertension.