Unlike angiotensin converting enzyme inhibitors (ACEI), few long-term studies have shown calcium antagonists to retard the progression of renal dysfunction. Our aim was to prospectively compare the effects of amlodipine and ACEI (enalapril) on renal function in hypertensive patients with renal impairment due to chronic glomerulonephritis and essential hypertension. A total of 72 hypertensive patients with serum creatinine (Cr) > 1.5 mg/dL were randomly allocated to treatment with either drug. During a 1-year period, 33% of the patients treated with ACEI dropped out due to adverse events, whereas 9% of patients with amlodipine dropped out. Data of 28 patients were available for analysis of more than 1-year follow-up. Reductions in blood pressure were comparable between the amlodipine (from 165/101 to 138/81 mm Hg) and ACEI groups. Serum Cr increased from 2.1+/-0.8 (SD) to 2.6+/-1.0 mg/dL with amlodipine (n = 16), but the difference was equivalent to that with ACEI (n = 12). Creatinine clearance (Ccr) in the moderate dysfunction group (basal Cr, 1.5 to 2.0 mg/dL) changed from 36+/-10 to 33+/-11 mL/min (not significant) with amlodipine, and the change was similar to that noted with ACEI. Annual declines in Ccr with amlodipine (-3.7 mL/min/year) and ACEI (-2.6 mL/min/year) were comparable, and both tended to be smaller than the annual decline in glomerular filtration rate reported in the Modification of Diet in Renal Disease study (-6 mL/min/year). Serum potassium was increased significantly (P < .01), from 4.5+/-0.4 to 5.3+/-0.8 mEq/L, only in the ACEI group. This 1-year prospective study demonstrated the effect of amlodipine on renal function to be likely the same as that of ACEI. Furthermore, amlodipine was better tolerated than ACEI for hypertensive patients with renal dysfunction.