An interim analysis of the AASK trial at three years demonstrates a renoprotective effect [slower decline in glomerular filtration rate (GFR), delayed onset of significant decrease in GFR, end-stage renal disease (ESRD) or death, and a decrease in urinary protein excretion] of the angiotensin converting enzyme (ACE) inhibitor, ramipril, as compared to the dihydropyridine calcium channel blocker (DHP-CCB), amlodipine, in patients with mild-to-moderate renal insufficiency. The beneficial effect occurred in the presence of similar levels of blood pressure control and was apparent in patients with proteinuric (beyond the threshold of "dipstick positive" proteinuria, 300 mg/day) and non-proteinuric hypertensive nephrosclerosis. At the time of the interim analysis, the effectiveness of the beta-blocker metoprolol was not significantly different from that of the ACE inhibitor. The data suggest that DHP-CCBs should be used with caution in the presence of mild-to-moderate renal insufficiency.