In 673 open fractures of long bones (tibia and fibula, femur, radius and ulna, and humerus) treated from 1955 to 1968 at Hennepin County Medical Center, Minneapolis, Minnesota, and analyzed retrospectively, the infection rate was 12 per cent from 1955 to 1960 and 5 per cent from 1961 to 1968. In a prospective study from 1969 to 1973, 352 patients were managed as follows: debridement and copious irrigation, primary closure for Type I and II fractures and secondary closure for Type III fractures, no primary internal fixation except in the presence of associated vascular injuries, cultures of all wounds, and oxacillin-ampicillin before surgery and for three days postoperatively. In 158 of the patients in the prospective study the initial wound cultures revealed bacterial growth in 70.3 per cent and the infection rate was 2.5 per cent. Sensitivity studies suggested that cephalosporin is currently the prophylactic antibiotic of choice. For the Type III open fractures (severe soft-tissue injury, segmental fracture, or traumatic amputation), the infection rates were 44 per cent in the retrospective study and 9 per cent in the prospective study.