This study was undertaken to test whether increasing the hydrophilicity of small-caliber polytetrafluoroethylene vascular prostheses by alcohol pretreatment or increasing their fibril length might improve their healing without affecting their patency. Polytetrafluoroethylene vascular prostheses (length 1 cm, inside diameter 1.2 mm) (1) with a fibril length of 30 microns (control group; n = 18), (2) pretreated with alcohol (n = 18), or (3) with a fibril length of 60 microns (n = 18) were implanted into the abdominal aorta of rats. The prostheses were evaluated by means of routine light and scanning electron microscopy during a 6-week period after implantation. All prostheses were patent at harvesting. On implantation, the control polytetrafluoroethylene vascular prostheses were only scarcely covered with platelets. At 6 weeks they had healed in a small area adjacent to the anastomoses only. In contrast, both the alcohol-pretreated polytetrafluoroethylene prostheses and the polytetrafluoroethylene prostheses with a fibril length of 60 microns were completely covered by a thin clot layer on implantation. At 6 weeks after implantation these prostheses had almost completely healed as a result of organization of the thin clot layer by ingrowth of both endothelial and smooth muscle cells. These results demonstrate that increasing hydrophilicity of polytetrafluoroethylene vascular prostheses by alcohol pretreatment or enlarging their fibril length improves their healing by induction of a thin luminal clot layer. This clot layer provides a suitable matrix for ingrowth of both endothelial and smooth muscle cells and does not lead to thromboembolic complications.