Blood flow through femoral-popliteal vein grafts in 15 extremities was compared with flow through 14 femoral-tibial grafts at the time of surgery. Average baseline flow was 98 ml/min in the femoral-popliteal and 99 ml/min in the femoral-tibial group. Intra-arterially administered papaverine produced an increase in average flow up to 176 ml/min in the former and 162 ml/min in the latter group, and the difference was not statistically significant. The effect of subsequent occlusion, or patency, the presence of diabetes, clinical severity of ischemia, and angiographic staging of runoff were correlated with graft flow within each group and between the two groups. A statistically significant adverse correlation could not be demonstrated for any of these factors.