Two separate angiographic studies were carried out in 96 patients early (2 weeks) and late (12-18 months) after aortocoronary vein grafting. Eleven of the initial 144 grafts were found to be occluded on the early study. Thirty of the remaining 133 grafts were occluded on the late study— a combined patency rate of 72 per cent. Most grafts displayed some reduction in size on the second study. Mean reduction was 30 per cent. This reduction in caliber was negligible to mild in 71 grafts, moderate (40 to 60 per cent reduction) in 29 grafts and was severe (> 80 per cent) in 3 grafts. In addition to the diffuse decrease in size, there were 36 instances of localized narrowing on the late study. This narrowing was mild in 19 grafts, moderate in 14 grafts and severe in 3 grafts. It is concluded that, although some degree of narrowing is to be expected in aortocoronary vein grafts after 1 year, certain factors are likely responsible for the more severe narrowing and for late thrombosis of vein grafts. Early and late angiographic studies can help the cardiologist and surgeon in the detection and prevention of the factors which, in some cases, may be responsible for late occlusion or stenosis of aortocoronary vein grafts.