Open fracture wounds may be contaminated, and the use of an appropriate antibiotic in the early stages of management reduces the risk of osteomyelitis developing. Environmental factors influence both the type of micro-organisms that are isolated from these wounds and the antibiotics that are chosen to manage the wounds. Before this study, the choice of antibiotic in the management of open fractures in our hospital was based on tradition and 'best guess' antibiotics. In a prospective study of 52 open fractures seen in the accident and emergency unit of University College Hospital, Ibadan, between January and June 2000, the positive bacterial culture yield was more than 70%. Staphylococcus aureus was the commonest microbial isolate, accounting for 37.5% of total isolates. The antibiotic sensitivity pattern revealed high efficacies for pefloxacin, ciprofloxacin and ceftriaxone against the isolated micro-organisms. In comparative costs, these antibiotics are cheaper than the combination of the 'best guess' antibiotics that were used previously. On the strength of this finding, we have suggested a change in the antibiotic policy of the hospital with regard to the antibiotic regimen to be used to complement the surgical management of open fractures.