The prospective clinical examination of 80 patients with the verified carcinoma of the colon and rectum was performed at the Clinic of General and Vascular Surgery of the M.M.A. in the period 1989-1990 with the aim to evaluate efficacy and justified use of antibiotic prophylaxis or prophylaxis and antibiotic therapy after elective surgical intervention. The preoperative mechanical preparation was performed in all patients. The combined metranidazole-gentamycin therapy was applied. In the group of patients receiving antibiotic therapy only, as a short prophylaxis, the postoperative infective complications were recorded in 5% of cases. In the second group of patients receiving antibiotic prophylaxis and therapy these complications were recorded in 10% of cases. The average duration of postoperative hospitalization was 13/14 days in both groups of patients. The use of antibiotic prophylaxis in elective colorectal surgery in patients with carcinoma of the colon and rectum is justified but it is not a substitution for nonadequate surgical intervention.