Varying lengths of femoral vein grafts from 36 New Zealand rabbits were used to bridge defects in the ipsilateral femoral artery in an attempt to estimate the correct length of vein graft needed to replace an arterial defect. Harvested venous segments contracted by 35% to 55% of their in vivo length. Short grafts subjected to linear tension had poor patency rates. Increasing the length improved patency. Long redundant grafts were initially tortuous, but lost their redundancy when studied long term. Silicone perfusion studies, however, revealed a persistence of luminal irregularity and tortuosity. Histologically, arterialized vein grafts thickened by accumulation of fibrous tissue in the medial layer, but otherwise maintained identifiable venous morphological characteristics. Scanning electron microscopic studies identified endothelial changes in vein grafts after arterialization. Based on these results, the ideal microvenous graft should be approximately 35% longer than the arterial defect to be bridged when measured in vivo to permit optimal balance between linear and radial deforming forces.