More than 40,000 new patients begin treatment for end-stage renal disease in the United States each year. The most frequent causes are diabetes and hypertension. The incidence rates for blacks and Native Americans are six- to sevenfold in excess of those for whites. Studies are seeking to determine the roles of atherosclerotic vascular disease, renal ischemia, and the amount of renal mass on the rate of progressive renal disease. Other studies seek to identify the factors that predict the development of nephropathy in patients with diabetes mellitus. Treatment of hypertension slows the rate of progressive renal disease by 40% to 50%. Meta-analysis of several European studies suggests that dietary protein restriction appears to delay the onset of end-stage renal disease.