Two hundred and forty one patients were included in a prospective randomized double-blind trial comparing the efficacy of three days(group 1,42 patients) versus that of five days cefotiam(group II, 199 patients) injection for prophylaxis against wound infection in patients who had an operation using bone plate, Ender of Kiintscher nails, or other internal fixation devides. The two groups were similar in terms of mean age, sex ratio, duration of preoperative hospital stay, underlying risk factors and type of surgical procedure. A wound infection developed in one of the forty-two patients in group I(2.3%) and in nine of 199 patients in group II(4.5%). This difference of infection rate is not stati stically significant(p>O.05). Staphylococcus aureus, Staphylococcus epidermidis , Klebsiella pneumoniae and Enterobacter aerogenes were the common infecting organisms. And the infection rate in lower extremity operations was higher than that of other regions in the group II (p In conclusion. the recommended method of administration of prophylactic antibiotics in clean orthopaedic surgery to prevent postoperative wound infection is a high dosage injection of antibiotics one hour before surgery, intraoperative infusion of one dosage when the operation lasts more than one hour and then postoperatively within 72 hours. This will reduce the adverse effects of medication and will also reduce the costs.