The efficacy of antibiotic prophylaxis in cardiac surgery was compared between 97 patients receiving a single 2 g dosage of ceftriaxone and 103 receiving 500 mg of vancomycin i.v. every 6 h for 48 h. The overall infection rate was 13.4% in the ceftriaxone and 10.7% in the vancomycin group. Four (4%) wound infections, including one mediastinitis, occurred in the ceftriaxone group and five (5%) in the vancomycin group, with no statistically significant difference. The findings of this study support the adequacy of a simple single dose of ceftriaxone prophylaxis in cardiac surgery, at least in hospitals with low incidence of vancomycin-resistant staphylococcal infections.