Circulating, locally generated angiotensin II plays a key role in cardiac, renal, and vascular structural changes. The aim of this study was to investigate the effects of losartan, an angiotensin II receptor (type AT,) antagonist, on cardiac and renal function and lipid profile in patients with essential hypertension. Forty patients (29 women, 11 men), mean age 51.9 +/- 10.2 years (range, 34 to 72 years), with mild-to-moderate essential hypertension were treated with losartan for 12 weeks. Before and after treatment, 24-hour urinary albumin excretion, serum electrolytes, serum Lipid profile, and creatinine clearance were measured. In addition, systolic and diastolic blood pressures and left ventricular mass were determined by Doppler and M-mode echocardiography. Radionuclide ventriculography was performed to assess ejection fraction. Mean arterial pressure decreased significantly from 121.9 mm Hg at baseline to 96.6 mm Hg after 12 weeks of treatment (P = 0.0001). Low-density Lipoprotein/ high-density Lipoprotein cholesterol ratio decreased significantly from 3.5 +/- 1.8 to 2.9 +/- 0.8 (P = 0.03). A significant reduction was found in left ventricular mass (from 186.9 +/- 41.3 g to 179.7 +/- 41.8 g) (P = 0.0001). No significant change in urinary albumin excretion was found after 12 weeks. We did not identify any serious side effects and did not find any significant change in serum electrolytes or systolic cardiac function. Although the decrease in creatinine clearance was statistically significant (P = 0.002), the mean creatinine clearance was within the normal range (96.01 +/- 16.3 mL/min); this change was not clinically significant. The effect of losartan on diastolic cardiac function was not clear. Results of this study suggest that losartan is an effective, safe agent in the treatment of essential hypertension and has beneficial effects on left ventricular mass and serum lipid profile.