The authors report the results of a multicentric clinical study on prevention of surgical infections in colorectal surgery by chemo-antibiotic prophylaxis. This trial was carried on to evaluate the effect of imipenem-cilastatin (1 g i.v. just before operation and 1 g i.v. 3 hours from surgical procedure) vs. cefuroxime + metronidazole (1.5 g + 0.25 g i.v.) or cefotetan (1 g i.v.) given with the same modalities. In 48 patients undergoing colorectal resection (47 with malignant neoplastic disease) 24 were treated with imipenem, 18 with cefuroxime and 6 with cefotetan. In group A (imipenem-cilastatin) the infection rate was 4.2% (1/24 cases), in group B (cefuroxime + metronidazole or cefotetan) postoperative infections were registered in 4 out of 24 cases (16.6%). This study documented the good results of systemic chemoprophylaxis and the great efficacy of imipenem-cilastatin in colorectal surgery.