Patients having arterial reconstructive operations appear to have a comparatively high attack rate of hospital-acquired infections. A protocol for administration of antibiotic prophylaxis to such patients was designed to minimize major adverse effects while evaluating the effect on attack rate of hospital acquired infections. Short intensive therapy with an appropriate antibiotic during a period of time surrounding the operative procedure itself is emphasized. The attack rate of nosocomial infections declined from approximately 12 to approximately 3 per cent and wound infections occurred in only seven of 811 patients. Administration of antibiotics according to this protocol appears to reduce the expected attack rate of nosocomial infections.