The purpose of this study was to investigate early arterial graft healing and its sources in porous Dacron prostheses after very short implantation periods in the dog, using extensive histologic examination of serial sections. Preclotted Dacron prostheses 6 cm long and 8 mm in diameter were implanted in the descending thoracic aorta (DTA) of 14 dogs, and retrieved at 7 days (n = 6), 10 days (n = 4), and 14 days (n = 4). The flow surface was assessed for thrombus coverage, endothelial-like cell (ELC) coverage, and the number of microvessel ostia. Where an ELC island was identified under the stereomicroscope, full-wall longitudinal tissue samples were taken, and embedded in resin for light microscopy study of 6-microns, H&E-stained serial sections to determine general healing and interstitial tissue presence. If there was more than one ELC island, another full-wall sample was taken and embedded in paraffin for staining with laminin, collagen IV, and smooth muscle alpha-actin antibodies, and PTAH. All grafts were patent with very little thrombus. Islands of endothelial-like cells were found for each time period, and on all 14-day grafts. Endothelial-like cell coverage was highest at 14 days. On 7- and 10-day grafts, cells proved to be endothelium were found in the middle of the flow surface, unconnected to either pannus or perigraft tissue ingrowth. Healing occurs as early as 7 days in porous knitted Dacron grafts. The source at periods earlier than 10 days appears to be cells from the blood stream.