In this open, prospective, comparative study, 75 patients who sustained penetrating abdominal trauma were randomised to receive 1 of 3 antibiotic regimens preoperatively and for 3 to 5 days postoperatively. Group I received cefotaxime 2g 8-hourly, group II received cefoxitin 2g 6-hourly and group III received clindamycin (900 mg 8-hourly) and gentamicin 3 to 5 mg/kg/day in divided doses 8-hourly. The 3 groups were not statistically different in terms of age, sex, severity of injury, number of organs injured, colon injuries, shock, blood transfusions or positive intra-operative cultures. Septic complications occurred in 8% of patients in group I, in 4% of group II patients and in 8% of group III patients. Cefotaxime was the least costly regimen, followed by cefoxitin, then clindamycin and gentamicin. It may be concluded that single agent therapy with a broad spectrum cephalosporin is preferable to combination therapy on the basis of equivalent effectiveness, less toxicity and lower costs.