Previous studies of saphenous vein (SV) bypass grafts have been either angiographic or morphologic, and few have correlated angiograms with histology. Nine necropsy patients who had received 21 SV implants 12 to 120 months (mean 67 +/- 42) before death were studied. All patients had severe coronary artery disease. Three types of histologic changes were found: atherosclerosis in 9 grafts, fibrointimal proliferation in 8 and total occlusion with fibrosis in 4. All patients had premortem angiograms 0 to 3 months (mean 0.7 +/- 1.1) before death. In 14 of 21 grafts, premortem angiograms accurately reflected the postmortem findings. In 7 grafts, the premortem angiograms either overestimated (4 grafts) or underestimated (3 grafts) the extent of luminal narrowing. Six of the 7 SV implants incorrectly assessed by angiography had fibrointimal proliferation and 1 had atherosclerosis. The presence of smooth muscle in SV implants with fibrointimal proliferation may be a mechanism of spasm or relaxation during angiography, which could cause errors in estimating the degree of stenosis. Nitrates or calcium antagonists may be useful in both assessing the degree of underlying vasomotion in SV grafts and as a therapeutic modality.