One hundred fifty patients undergoing cesarean section were evaluated prospectively for the effect of prophylactic antibiotics on postoperative morbidity. The postoperative infection rate was significantly reduced, being 30%, 16%, and 50% in the ampicillin, the cephalothin, and the control groups, respectively. The results are favorably compared with the results achieved in previously reported studies where the antibiotic treatment was started preoperatively. Our study confirms experimental studies that postoperative infection can be reduced by using prophylactic antibiotics in the immediate postoperative period. By this regimen, undesired placental transfer of the antibiotics to the fetus can be avoided.