A woven, double velour Dacron vascular graft was made nonporous by coating it with a layer of collagen prepared from fresh, young calf skin. Grafts were implanted in the thoracic aorta of 24 mongrel dogs and were examined at intervals up to 180 days. The grafts did not require preclotting or special preparation before being implanted. They sutured easily and did not bleed. When explanted all grafts were patent and covered with neointima. The bovine collagen was almost completely resorbed by 90 days and was replaced with native tissue. The collagen was neither thrombogenic, antigenic, cytotoxic, or pyrogenic.