Quinapril is a monoethyl ester which is hydrolysed after absorption to form an active metabolite, quinaprilat, which is a more potent angiotensin converting enzyme (ACE) inhibitor than the parent drug. Quinaprilat has a short elimination half-life but a potent binding affinity for ACE which enables once daily administration. Data from clinical studies indicate that quinapril 10 to 40 mg daily, given as a single dose, is an effective antihypertensive agent, suitable as monotherapy for reducing high blood pressure and maintaining satisfactory control during long term treatment of mild to severe hypertension. Dosages of 80 mg daily have been used in some patients. Concomitant diuretic therapy usually elicits a response in patients who fail to respond adequately to monotherapy. Initial studies suggest that quinapril also has a role in the treatment of mild to severe congestive heart failure. In the few long term studies conducted the beneficial acute haemodynamic effects were maintained during long term treatment and were accompanied by symptomatic and functional improvement. The majority of these patients responded to twice daily administration. Adverse effects associated with the antihypertensive action of quinapril are generally mild, well tolerated and are similar to those of other ACE inhibitors. Thus, quinapril appears to be a useful alternative ACE inhibitor for the treatment of mild to severe hypertension and congestive heart failure.