To assess the efficacy of single-dose antibiotic prophylaxis in coronary artery bypass grafting, 1,016 consecutive patients were prospectively randomized to receive either a single dose or a three-day course of cefuroxime. Nine patients (0.9%) died within seven days; no death was caused by infection. For various reasons 163 other patients were not evaluable. Therefore, 844 patients were evaluated. Patients in group A (n = 419) received 20 mg/kg cefuroxime intravenously at induction of anaesthesia; group B (n = 425) received the same dose followed by 750 mg t.i.d. for three consecutive days. Both groups were comparable regarding all risk factors. The efficacy of the prophylactic regimens was evaluated by comparison of occurrence of wound infection in both groups. No significant differences in wound infection were observed between the two treatment groups: sternal site infection in the single-dose prophylaxis group was 14% versus 13% in the three-day course group; donor site infection occurred in 38% versus 39%. It is concluded that in coronary artery bypass grafting a single dose of cefuroxime is as effective as a three-day course in the prevention of wound infection.