Thirty-three cats' femoral and carotid arteries repaired and grafted with microsuture techniques were examined histologically 11 to 23 months following surgery. Scar tissue was found at the site of longitudinal and circumferential repairs. Vein-patch grafts were completely replaced by fibrous tissue, and a new internal elastic lamina had developed. Segmental and bypass grafts maintained their three vascular layers, but some degree of fibrosis developed at all levels. The reason for the difference between the behavior of the vein patch and the segmental vein graft when implanted in an artery may lie in the ratio of surgical trauma to the size of the graft.