This study investigated the efficacy of perioperative antibiotics in preventing bacteremic infection of vascular suture lines, Dacron grafts, and bovine heterografts. One hundred forty-nine dogs had either segmental excision of the abdominal aorta with primary repair, Dacron prosthesis, or bovine heterograft placement. Animals were randomly assigned to a control group, to receive 10(8) S aureus, or to receive this same dose of staphylococci plus cephalothin (15 mg/kg). After six weeks, graft cultures were obtained. All control animals had negative cultures. Often dogs with an aortic suture line subjected to bacteremia, five were infected. Eight dogs with aortic suture lines received bactermia and antibiotics resulting in only one positive culture. Nineteen animals with bovine grafts were given S aureus resulting in 18 infections, and seven of 12 bovine grafts became infected even with antibiotic coverage. Twenty-eight dogs had a Dacron graft and infusion of Staphylococcus, yielding 23 infections. Of the 24 Dacron graft subjects with induced bacteremia and antibiotics, only four were infected. Intraoperative antibiotics are significantly effective in preventing infection of vascular suture lines and Dacron prostheses but afford less protection to bovine heterografts.