A total of 84 grafts 100 mm in length was inserted as arterial and shunt conduits in 31 mongrel dogs. There were 24 glutaraldehyde pre-treated vein bypass grafts, 15 glutaraldehyde pre-treated vein shunt grafts, 9 fresh, untreated vein bypass grafts, 10 combined teflon-glutaraldehyde pre-treated vein shunt grafts, 11 glutaraldehyde pre-treated umbilical vein shunt grafts, 11 glutaraldehyde pre-treated umbilical vein bypass grafts, 4 dacron mesh covered modified umbilical vein bypass grafts. The internal diamter was 4 mm in all the saphenous vein grafts and in seven of the umbilical vein grafts and 6 mm in all other grafts. After an implantation period of 0.5--2.5 months, 5 of the 24 glutaraldehyde pre-treated saphenous vein bypass grafts were patent, and the rest thrombosed. These grafts were very adherent to surrounding structures. Glutaraldehyde pre-treated saphenous vein shunt grafts occluded within 2.5 months. Combined teflon-glutaraldehyde pre-treated saphenous vein shunt grafts functioned better, 6 of 10 grafts being patent after 4.0--6.0 months. Eight of 9 fresh grafts were thrombosed within one month. Eleven glutaraldehyde pre-treated human umbilical vein bypass grafts were followed up for 5.0 months and both those with a 4 mm internal diameter and those with 6 mm functioned well. Glutaraldehyde pre-treated human umbilical shunt grafts also functioned well up to 5.0 months. Reactive changes were minimal around umbilical grafts.