Six bilateral loop arteriovenous fistulas from the femoral artery to the femoral vein were constructed in dogs using Dacron-mesh-coated human umbilical vein. Each graft was punctured twice weekly with a 16 gauge needle for up to 36 weeks, and biopsies were done every four to eight weeks. The long-term patency was 83% at 24 weeks. There was no thrombosis from the needle puncture. Serial histologic examination revealed progressive transmural fibrous cell ingrowth and progressive neointimal cell formation. Scanning electron microscopy demonstrated areas of disrupted basement membrane covered with laminar fibrin meshes, probably representing sites of needle puncture. With multiple attenuated internal reflection spectroscopy of the graft lumens, minimal to moderate lipid deposition was observed to a depth of 1 micrometer at 32-36 weeks. No abnormal amounts of minerals were found within the graft walls with energy-dispersive x-ray analysis. Critical surface tensions remained within the biocompatible range of 20-30 dynes/cm. Human umbilical vein possesses many of the surface chemistry qualities of an ideal vascular prosthesis, has excellent long term patency, and is suitable for use where angioaccess with repeated needle puncture is needed.