OBJECTIVE To study the effects of the angiotensin II antagonist losartan in hypertensive patients with renal disease. METHODS A single-blind longitudinal study was performed, lasting 4 months. Patients were treated once a day with placebo, 50 mg losartan, 100 mg losartan and placebo, each for 1 month, in sequence. Measurements were taken at the end of each treatment period. METHODS The study subjects comprised 13 patients with biopsy-proven renal disease, a diastolic blood pressure of > 90 mmHg, creatinine clearance of > 60 ml/min and stable proteinuria of > 2.0 g/day. RESULTS Mean arterial pressure, measured 4 h after the dose, fell from 113.8 +/- 2.1 mmHg (placebo) to 99.2 +/- 2.4 mmHg (50-mg dose) and 96.5 +/- 2.4 mmHg (100-mg dose). This blood pressure lowering effect was sustained for 24 h 116.3 +/- 2.3 mmHg (placebo) versus 105.5 +/- 1.8 mmHg (50-mg dose) and 103.3 +/- 1.9 mmHg (100-mg dose)]. The glomerular filtration rate remained stable, while the effective renal plasma flow increased by 12.5 +/- 2.9% (100-mg dose). The systemic and renal hemodynamic effects were similar at the 50- and 100-mg doses. Urinary excretion of total protein, albumin and immunoglobulin G decreased dose-dependently by a maximum of +/- 50% (100-mg dose). With the high dose, serum uric acid fell from 0.43 +/- 0.02 mmol/l to 0.39 +/- 0.02 mmol/l, and potassium increased from 4.2 +/- 0.1 to 4.6 +/- 0.1 mmol/l. CONCLUSIONS The angiotensin II antagonist losartan lowers blood pressure and displays a favorable renal profile in hypertensive patients with renal disease.