To clarify the structural changes of saphenous vein grafts after coronary artery bypass grafting, intravascular ultrasound and angioscopic images were obtained from 23 grafts in vivo and 5 grafts and 3 new veins in vitro; the images were compared with histologic findings. Intravascular ultrasound demonstrated a single-layered appearance at new veins and all of the angiographically normal grafts within 6 months after surgery. A triple-layered appearance that might be related to the remarkably proliferative and degenerated intima was revealed histologically at 73.3% of the normal sites of grafts between 5 and 10 years after operation. In 83.3% of the stenoses at several years after operation, angioscopy showed yellow atheromatous plaques, often with a friable surface; a heterogeneous, lucent echo pattern was revealed on intravascular ultrasound. Thus intravascular ultrasound and angioscopy may be used to identify the morphologic changes of graft at different points after implantation more precisely than conventional angiography.