One hundred and ninety-five patients undergoing abdominal surgical procedures completed a multicentre, randomized, open-label study comparing the safety and efficacy of cefmetazole and cefoxitin for the prevention of postoperative wound infection. Cefmetazole was administered iv in a single 2 g dose given within 90 min of the operation. Cefoxitin was administered in a single 2 g, similarly timed, preoperative dose and two additional doses given at 6 h intervals after surgery. For operations that exceeded 2-4 h duration an additional dose of each agent was administered. Patients undergoing colorectal operations received oral neomycin and erythromycin as bowel preparation. Colorectal operations were performed most frequently (49% of patients) followed by cholecystectomies (26%) and gastroduodenal procedures (21%). The operative site infection rate was 6-5% for cefmetazole and 7-7% for cefoxitin (P >0 05). Serious drug related adverse effects were not observed. This study demonstrates that administration of single-dose cefmetazole is as effective as a standard three dose regimen of cefoxitin for prophylaxis with abdominal operations.