There are chemical differences among angiotensin-converting enzyme (ACE) inhibitors that profoundly influence the pharmacokinetics and dynamics of different drugs. Differences in potency, affinity, and duration of action can be readily identified. These factors, together with individual binding characteristics of drug (or metabolite) to ACE, may influence the profile of hemodynamics and adverse effects, including first-dose hypotension and renal impairment. Differential inhibition of ACE in tissues (e.g., heart, brain, adrenal, kidney, blood vessel) could be important in identifying a particular ACE inhibitor for a specific clinical indication.