Data from the Brachial Artery Normalization of Forearm Function (BANFF) trial indicate that angiotensin-converting enzyme (ACE) inhibitors and other vasoactive substances appear to differ in their ability to improve endothelial dysfunction. Only quinapril, which is a lipophilic ACE inhibitor with high affinity for tissue ACE, produced a significant improvement in flow-mediated brachial artery dilation in coronary artery disease patients; enalapril, losartan and amlodipine did not. Quinapril showed highly significant improvement in subjects with one copy of the insertion allele, either the ACE-ID or the ACE-II genotype. It is anticipated that the effects of QUinapril On Vascular ACE and Determinants of ISchemia (QUO VADIS) trial will further differentiate ACE inhibitors (quinapril versus captopril) according to their effects on vascular tissue taken from pretreated patients undergoing coronary artery bypass graft surgery.