This review discusses important issues related to the use of angiotensin-converting enzyme inhibitors (ACEIs). ACEIs have been shown in clinical trials to slow progressive renal, cardiac, and vascular disease. The Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recommends ACEIs as alternative first-line therapy in patients with essential hypertension (HTN), congestive heart failure, and in hypertensive diabetics who also have renal disease. Many of the therapeutic benefits derived from ACEIs are thought to be class effects. There are certain distinctive pharmacokinetic and pharmacodynamic features for some of the ACEIs such as differences in absorption, protein binding, half-life, and metabolic disposition. In appropriate doses, they all lower blood pressure similarly. In the treatment of HTN and hypertensive renal disease, a class effect appears to be applicable when selecting an agent. It is less likely that ACEIs are interchangeable in the treatment of congestive heart failure because maximal cardioprotective tissue effect rather than blood pressure normalization is the goal. In addition, for some agents clinical trials that demonstrate decreased morbidity or mortality are currently lacking.