Recent studies showed high populations of both aerobes and anaerobes in penetrating abdominal trauma infections. Combined aminoglycoside-clindamycin therapy has resulted in infection rates of 7 to 10 per cent. However, high side-effect incidences of nephrotoxicity and ototoxicity have been attributed to the aminoglycosides. Cefoxitin is reportedly free of these side effects. In our study, 62 penetrating abdominal trauma patients requiring laparotomy were treated with cefoxitin pre- and postoperatively. The majority of the injuries, 75.8 per cent, involved small bowel and large bowel. Infections occurred in four patients of the total 62 (6.5%). Two side effects, a fever and a rash, subsided immediately after discontinuing cefoxitin; no ototoxicity or nephrotoxicity occurred. The safety and efficacy of cefoxitin alone versus aminoglycoside-clindamycin combination therapy was statistically compared in intestinal injuries only among two historical controls and our subgroup. Our infectious rate, 8.5 per cent, was comparable to 7.4 per cent and 10.4 per cent of the historical controls. We concluded that pre- and postoperative use of cefoxitin alone is as effective in the prevention of penetrating abdominal trauma infections as combined aminoglycoside-clindamycin therapy. Experience to date suggests that the use of a beta-lactam antibiotic such as cefoxitin may allow the physician to avoid the more serious side effects associated with the use of aminoglycosides in these patients.