Effects of losartan and amlodipine on blood pressure and albuminuria were compared in a randomized, double-blind, parallel trial involving 48 patients with essential hypertension (sitting diastolic blood pressure between 95 to 115 mm Hg) and impaired renal function (creatinine clearance of 30 to 60 ml/min/1.73 m2). After four weeks of placebo administration, patients were stratified according to baseline albuminuria (< or > or = 300 micrograms/min) and randomized to once-daily treatment with losartan 50 mg (N = 24) or amlodipine 5 mg (N = 24) for 12 weeks. Titration to losartan 50 mg/hydrochlorothiazide (HCTZ) 12.5 mg or amlodipine 10 mg was possible at weeks 3 or 6 for patients having an inadequate blood pressure response. After 12 weeks of treatment, the mean decreases in sitting diastolic and systolic blood pressures were significantly larger in the losartan group (-18.1 +/- 7.2 and -27.7 +/- 15.2 mm Hg) than in the amlodipine group (-12.4 +/- 7.5 and -16.3 +/- 12.1 mm Hg; P = 0.009 and P = 0.008, respectively). The greater antihypertensive response to losartan was not influenced by the initial degree of albuminuria. The losartan and amlodipine regimens were well-tolerated. Baseline levels of albuminuria were reduced after 12 weeks of losartan treatment (median change of -29.5 micrograms/min), while amlodipine therapy was associated with a median increase (48.4 micrograms/min) in this renal marker at week 12. The treatment difference was statistically significant (P = 0.021). These results indicate that losartan 50 mg, administered alone or in combination with HCTZ 12.5 mg, is more effective than amlodipine 5/10 mg in lowering blood pressure and albuminuria in patients with essential hypertension complicated by impaired renal function.