Abstract--This study was performed to compare the effects of nifedipine retard and angiotensin-converting enzyme (ACE) inhibitors on the progression of coronary atherosclerosis by means of quantitative coronary angiogram. Coronary angiogram was performed before the start of the study and during the 3-year treatment period. This study was conducted on the assumption that possible coronary vasodilation, which may be caused by nifedipine, was excluded by administration of sufficient isosorbide dinitrate. The changes from the baseline in the minimum lumen diameter of the coronary artery in all measured segments were negligible in the nifedipine group (+0.02±0.27 mm; P=0.543), whereas they were significantly reduced in the ACE inhibitor group (-0.12±0.27 mm; P<0.001), with a significant difference observed between the groups (P=0.002). The number of progressors in the nifedipine group was significantly lower than that in the ACE inhibitor group (P=0.019), and there was also a significant difference between the groups in the number of patients in whom 1 lesion developed after treatment (P=0.040). However, the changes of minimum lumen diameter stratified by baseline percent diameter stenosis demonstrated that progression of coronary atherosclerosis was suppressed in the nifedipine group for lesions with a percent diameter stenosis of 40 but was suppressed in both groups for those with a percent diameter stenosis of 41. This study suggests that nifedipine retard and ACE inhibitors may be effective in suppression of progression of coronary atherosclerosis, and that nifedipine in particular may be effective for mild to moderate stenosis.