Angiotensin converting enzyme (ACE) inhibitors are increasingly used to treat hypertension and congestive heart failure. Recently, several new ACE inhibitors with pharmacokinetic features different from earlier agents such as captopril or enalapril have come into use. This review discusses the use of pharmacokinetics to optimise ACE inhibitory therapy in various patient groups. Among the pharmacokinetic characteristics of ACE inhibitors the route of excretion and to a lesser degree the half-life appear to be the most clinically relevant. There is no evidence that being a prodrug offers a significant clinical advantage. The importance of varying tissue penetration also remains to be determined. Knowledge of ACE inhibitor pharmacokinetics is particularly important in patients with renal or hepatic dysfunction in whom the major route of excretion of these agents is impaired. This might also be the case in elderly patients or those with severe congestive heart failure. However, for most ACE inhibitors, major changes in the drug dosage (amount or interval) are necessary only when the glomerular filtration rate falls below 30 ml/min (1.80 L/h). The occurrence of adverse effects due to overdosage or drug interactions may be prevented by adapting the prescription of an ACE inhibitor to its pharmacokinetic characteristics.