Development of a small caliber biologic vascular graft: evaluation of its antithrombogenicity and the early healing process. The authors previously showed that a small caliber xenograft using our crosslinking technique was applicable to aortocoronary bypass grafting. In this study of the graft, the antithrombogenicity and healing process was evaluated at an early stage after implantation. Fresh sheep carotid artery (3mm ID) was obtained and cross-linked with polyepoxy compounds, and then used as a small caliber vascular graft. The graft was white and soft. Six cm segments of the graft were implanted into the carotid arteries bilaterally in nine dogs. Sodium heparin was given during the surgery, but no anticoagulant was used postoperatively. Fifteen grafts from eight dogs were removed from 1 hr to 30 days after implantation, and 13 of 15 grafts were found to be patent. Two grafts, one at 3 days, and the other at 14 days, were occluded. The anastomotic area of the occluded grafts felt hard when touched from the outside. In one dog, the grafts were shown angiographically to be patent at 14 days after implantation, and this dog was kept for long-term observation. Macroscopically, no thrombus was observed on any of the patent grafts. Microscopically, the inner surface near the anastomotic lines was covered with endothelial cells, and infiltration of fibroblasts was observed from the outside 7 days after implantation. No foreign body reactions were seen around the graft. After 30 days of implantation, a thin layer of plasma protein at the middle of the graft was observed by scanning electron microscopy (SEM). From these observations, it was concluded that the grafts exhibited satisfactory early antithrombogenicity and healing after implantation. 