The effect of suture material on healing of vascular anastomosis was examined. Four types of vascular grafts, i.e., autogenous vein, preserved human umbilical cord vein, expanded polytetrafluoroethylene and double velour knitted Dacron, were implanted into the abdominal aorta of 78 adult mongrel dogs using two kinds of absorbable sutures (multifilament polyglycolic acid: PGA and monofilament polydioxanone: PDS) and a nonabsorbable suture (polypropylene: PP). The macroscopic findings and the histologic examinations showed that hyalinoid degeneration and calcification resulting from tissue ischemia due to tight and long lasting suture loops interfered with tissue healing at the PP-anastomotic site. On the other hand, fairly good healing of the anastomoses was observed with absorbable sutures because of the reduction of ischemia. The absorbable suture-anastomoses could tolerate systemic blood pressure within one month after implantation, and there was no anastomotic disruption at 1000 mmHg pressure in the bursting test 12 months after grafting. From Dec., 1984, 55 anastomoses in 34 bypass-operations employing autogenous vein grafts were performed using PGA and PDS in 28 cases clinically. There were no anastomotic complications. In conclusion, the synthetic absorbable suture material, especially in the form of monofilament, seems to be most suitable for suturing or anastomosing autogenous small vessels at present.