Of the 1,396 patients who underwent gastroenterological surgery at our department in the past seven years, 132 (9.5%) developed surgical wound infections. The incidence of such infections varied greatly depending on the location and method of the operation. The causative organisms isolated from these infections were often the same as the normal bacterial flora in the organ that was the object of the surgery. Frequent factors of intra-abdominal infection, of which there were 62 cases, were leakage and intra-abdominal bleeding after extended operations in a compromised host. Antibiotics are not substitutes for careful surgical technique. For Escherichia coli and Klebsiella isolated from clinical specimens, we found that the antibiotics Cephalothin and Cefazolin did have satisfactory antibacterial activity. The first and second generation cephems seem suitable for use as prophylactic antibiotics against surgical wound infection. The best time to start giving prophylactic antibiotics was during the operation. Useful indicators of postoperative infection are the fever index, leucocytosis, CRP, and the erythrocyte sedimentation rate.