A bovine collagen graft was implanted in 30 dogs for the replacement of the femoral vein, the iliac vein and the inferior vena cava. During the observation period up to 210 days six thromboses of the graft were observed. Histological results after 30 days: development of a "neo-intima" with collagen type III, originating from the anastomosis. After 90 to 210 days: Continuous endothelial layer of the graft with appearance of smooth muscle fibers in the neo-intima. From the graft bed there was found resorption of the bovine collagen and replacement by new collagen type III fibers.