Atherosclerosis is the buildup of fats, calcium, and other substances within the walls of arteries. Localized atherosclerotic deposits, known as plaques, can obstruct arterial blood flow. Obstructed arteries are often treated by surgical implantation of vein grafts, which bypass the obstructed arteries and restore blood flow. In our rabbit vein graft gene therapy model, we consistently observed diminished blood flow over time. We hypothesized that this decrease was caused by narrowing at the ends (anastomoses) of the vein grafts, a phenomenon that is known as anastomotic stenosis and can be caused by vascular injury or poor surgical technique. Because decreased blood flow can interfere with vein graft function, we designed an experiment to test whether anastomotic stenoses were present and—if so—whether the stenoses were the cause of decreased blood flow. To test this hypothesis, in a new set of grafted veins, we harvested the anastomoses, embedded, sectioned, and stained them, and measured the percentage stenosis using computer-assisted image analysis. We measured the stenoses in both anastomoses of 44 vein grafts, harvested from 22 rabbits (88 total anastomoses). Blood flow (mL/minute) in each vein graft was measured with a flow meter 1 month after grafting and again 12 weeks later (at harvest). The mean change in blood flow was -16 mL/minute (range: -55 to 14) and the mean stenosis was 39% (range 2.3% to 89%). After confirming the presence of the stenoses, we used a nonparametric correlation test to examine our hypothesis that percentage stenosis and blood flow change were inversely correlated. We found that percentage stenosis did not correlate with blood flow change (r=0.059; P=0.8). Therefore, decreased blood flow in our vein graft model is not caused by anastomotic stenoses. The cause of the decreased blood flow remains uncertain, and other explanations may be considered.