Activation of the renin-angiotensin system during cardiopulmonary bypass (CPB) may be involved in early postoperative hypertension after coronary artery bypass grafting (CABG). As hypertensive episodes may be deleterious in the immediate postoperative period, we have assessed the effects of prophylactic treatment with the angiotensin-converting enzyme inhibitor quinaprilat in an open study. During steady state CPB, patients received quinaprilat 0.02 mg kg-1 (group A, n = 10), quinaprilat 0.04 mg kg-1 (group B, n = 10) or saline solution (group C, n = 10) as an i.v. bolus dose. Sodium nitroprusside (SNP) was given after operation when systolic arterial pressure was > 150 mm Hg. Requirements for SNP 1 h after arrival in the ICU were significantly less in groups A (two of 10) and B (two of 10) than in group C (eight of 10). Also, patients in group C had a greater systolic arterial pressure compared with groups A and B. There were no significant differences between groups in diastolic arterial pressure, heart rate, cardiac index or cardiac filling pressures. We conclude that quinaprilat can be used during CABG to reduce the incidence of postoperative hypertension. Further studies of the efficacy and safety of this technique are necessary.