In recent years, considerable attention has focused on the possibility that some classes of antihypertensive agents may confer a greater renoprotective effect in retarding the progression of chronic renal insufficiency. Experimental studies in rats have demonstrated that the sustained increase in glomerular capillary pressure evoked in response to loss of renal mass produces a destructive sclerosing reaction. Administration of angiotensin-converting enzyme inhibitors decreases glomerular capillary pressure with a resultant reduction of glomerular sclerosis, suggesting that angiotensin-converting enzyme inhibitor therapy may protect the injured kidney from hemodynamically mediated glomerular damage. On the basis of these experimental observations, many studies have attempted to investigate whether angiotensin-converting enzyme inhibitors can slow the progression of chronic renal disease in humans. We surveyed the literature critically and concluded that, the data from animals notwithstanding, the majority of studies in humans have been nonrandomized, of too short duration, or confounded by investigative difficulties. Therefore, we cannot yet conclude that angiotensin-converting enzyme inhibitors modify the rate at which renal disease progresses in nondiabetic patients.