This study was undertaken to assess the efficacy and safety of a 3-day course of treatment with Mefoxitin (cefoxitin sodium, MSD) in patients with perforated or ruptured appendicitis. A series of 235 patients undergoing surgery for perforated or ruptured appendicitis were treated with cefoxitin for 3 days. Twenty-four patients (10%) developed wound infection and 28 (12%) developed an intra-abdominal abscess postoperatively. No side effects were observed during the study. Compared with the results of our previous series, where a 5-day course of cefoxitin was used, the incidence of wound infection was similar. However the incidence of intra-abdominal abscesses in the present series was significantly higher (p less than 0.01). The results seem to indicate that a 3-day course of cefoxitin is as effective as a 5-day course in controlling the incidence of wound infection following surgery for perforated or ruptured appendicitis, whereas the 3-day course seems to be inferior to a 5-day course in controlling the incidence of intra-abdominal abscesses.