Bovine arterial heterografts and autogenous veins were compared as femoral artery bypass grafts in 33 dogs observed from 1 to 39 weeks. The vein grafts had a patency rate of 97%. Glutaraldehyde and dialdehyde tanned bovine grafts had patency rates of 13% and 50%, respectively. The poor performance of the heterografts was associated with marked fibrous hyperplasia at the anastomoses. It was concluded that autogenous vein remains the material of choice for small vessel bypass procedures.