The risk factors for sepsis after vascular surgery were studied in 100 consecutive patients with lower limb arterial ischaemia. Patients were randomised either to a short or long course of antibiotic prophylaxis with amoxycillin/clavulanic acid combination (Augmentin). Pathogenic organisms were isolated from the skin preoperatively in 39 (36%) cases, significantly more frequently in patients with ischaemic rest pain and skin necrosis (66%) than rest pain alone (21%) (P = 0.0004) or claudication/aneurysm (11%) (P = 0.0001). All but three organisms isolated (5%) were sensitive to amoxycillin/clavulanic acid. A wound infection occurred after 21 (19%) reconstructions, significantly more frequently both in patients suffering rest pain with skin necrosis (P = 0.001) and rest pain without skin necrosis (P = 0.04) compared with claudication/aneurysm. Sixteen of the 21 patients with a wound infection had at least one organism isolated from their skin preoperatively (P = 0.0001). Twelve patients (57%) had a similar organism isolated from the skin preoperatively and from the postoperative wound infection. Reducing the course of antibiotic prophylaxis from 5 days to 3 doses did not significantly increase the infection rate. The only other significant risk factor for sepsis was increasing age of the patient. Although prophylaxis is undisputed in patients having synthetic grafts, antibiotics may not be as important in the prevention of wound sepsis as had been thought. The role of antiseptic agents requires further evaluation.