Recent reports indicate that most coronary events originate from plaques causing <50% diameter stenosis. A subgroup analysis of the Bezafibrate Coronary Atherosclerosis Intervention Trial (BECAIT) data was undertaken to determine the effects of bezafibrate in relation to baseline narrowing. BECAIT included 92 male postacute myocardial infarction patients <45 years of age. Each received double-blind treatment with bezafibrate (200 mg 3 times daily) or placebo for 5 years, together with a low-fat diet. Coronary angiography was performed at baseline and after 2 and 5 years. The mean minimum lumen diameter of lesions causing 20% to <50% diameter stenosis at baseline did not narrow over 5 years in the bezafibrate group and decreased by 0.15 mm in the placebo group (p <0.05). In segments with > or =50% diameter stenosis at baseline, no change was seen in either of the 2 groups. In the analysis including only segments with 20% to <50% stenosis at baseline, coronary events were seen in 7 of 40 patients with a progression in minimum lumen diameter of more than the median value and in 3 of 41 patients with a change less than the median value. Thus, bezafibrate had a preferential effect in slowing the progression of narrowings causing <50% stenosis at baseline in young men followed up for a 5-year period after acute myocardial infarction.