The effectiveness of prophylactic cefoxitin in preventing postcesarean section infection was studied in a high risk population. One hundred women were evaluated, and on a random double-blind basis 50 received placebo and 50 received cefoxitin. There were three doses of drug given intravenously, either placebo or 1 gram of cefoxitin at the time of cord clamping and again four and eight hours later. Those receiving cefoxitin had significantly less postoperative infections, fewer had bacteremia and there was less postoperative fever as measured by the fever index. The patient with the most protracted infection in this study received cefoxitin. Problems with the use of systemic antibiotic prophylaxis in preventing postcesarean section infection are discussed. Cefoxitin is an effective agent to use in patients undergoing cesarean section who are at high risk for infection.