This report reviews our experiments that have been undertaken to test the hypothesis whether the induction of a clot layer on the graft surface of small-caliber polytetrafluoroethylene (PTFE) prostheses might improve their healing. PTFE prostheses with a fibril length of 30 microns, PTFE prostheses with a fibril length of 30 microns and either impregnated with Chitosan, or pretreated with alcohol or mechanically roughened, and PTFE prostheses with a fibril length of 60 microns (all prostheses: length 1 cm, ID 1.5 mm) were implanted into the abdominal aorta of rats and were evaluated from 1 day up till 6 weeks after implantation with regard to the presence or absence of a clot layer and with regard to the amount of graft healing. All untreated PTFE prostheses were never found to be covered with a clot layer and showed poor neoendothelial healing: even at 6 weeks after implantation, there were only endothelial cells near the anastomotic sides, directly on the graft surface. In contrast, all other PTFE prostheses were completely covered with a clot layer upon implantation and demonstrated almost complete neoendothelial healing after 6 weeks. Moreover, in these prostheses, the endothelial cells were present on a matrix of smooth muscle cells. These results confirm our hypothesis that the induction of a clot layer on the graft surface of PTFE prostheses improves their healing: the clot probably functions as a provisional matrix for the regeneration of arterial wall tissue, just as occurs in normal arterial wall repair.