In September, 2000, the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health called an early halt to the amlodipine arm of the African American Study of Kidney Disease and Hypertension (AASK) trial after careful deliberation by an independent data and safety monitoring board. An interim analysis of the AASK at 3 years revealed a renoprotective effect of the angiotensin-converting enzyme inhibitor ramipril as compared to the dihydropyridine calcium channel blocker (DHP-CCB) amlodipine in patients with mild to moderate renal insufficiency. This differential effect was independent of the blood pressure levels reached and was evident in both proteinuric and non-proteinuric patients with hypertensive nephrosclerosis. The AASK trial data suggest that DHP-CCBs should be used cautiously in the presence of mild to moderate renal insufficiency. Judgment should be reserved for the use of other CCBs, such as verapamil or diltiazem, since these are fundamentally different CCBs with the potential for a different impact on hypertensive nephrosclerosis. The blinded observation period for AASK will be completed at the end of September, 2001, at which time additional, clinically useful information is expected to become available.