Angiotensin-converting enzyme (ACE) inhibitors are a type of medication used to treat high blood pressure. The ACE inhibitors have clearly been shown to prevent worsening of kidney disease caused by diabetes. Some studies suggest that ACE inhibitors benefit nondiabetic people with kidney disease, while other studies do not. More than 350,000 people in the United States have end-stage kidney disease and require either dialysis, a procedure that filters the blood through an artificial kidney machine, several times a week, or a kidney transplant to stay alive. It is important to know whether ACE inhibitors might prevent worsening of kidney disease and keep some people from needing dialysis and transplantation.