A novel canine model for reliably producing graft thrombosis is described. Two unilateral aortoiliac bypasses are performed while preserving the integrity of the native vascular tree. These grafts are briefly mechanically occluded at the time of the initial operation, and they remain occluded postoperatively because flow is preferentially directed through the largercaliber, thrombo-resistant native circulation. Percutaneous temporary intra-arterial balloon occlusion of the native vessels redirects flow into the occluded graft segments, which can be used in experimental protocols. This new model for studying graft thrombosis requires only a single, simple operative procedure, and easily allows secondary percutaneous graft manipulation.