This study was designed to assess the role of macrophages in saphenous vein graft disease after coronary artery bypass grafting (CABG). Three newly harvested saphenous vein grafts (SVGs) and 6 SVGs removed from patients 8 to 15 years after CABG (3 were occluded soon after the operation and 3 became diseased after a long period) were immunostained for macrophages and investigated microscopically. No macrophages were detected in the newly harvested SVGs. In the grafts with early occlusion, macrophages were detected only in the superficial layer of the intima. In the grafts that became diseased after a long period, macrophage accumulation was detected at the site of atherosclerotic lesions. In the pathogenesis of arterial atherosclerotic lesions, vascular endothelial cell damage and subsequent subendothelial migration of monocytes/macrophages in the early phase are thought to be very important. This study revealed that macrophage migration into the intima of SVGs occurs soon after surgery and suggested it could be the basis of saphenous vein graft disease occurring long after CABG.