The safety and effectiveness of a single 2 g preoperative dose of cefotetan to reduce postoperative infectious complications after colorectal surgery was compared with multiple 2 g perioperative doses of cefoxitin in 289 patients enrolled in a multicenter trial; of the 239 evaluable patients, 164 received cefotetan and 75, cefoxitin. No statistically significant difference was detected in the successful clinical response rates for cefotetan and cefoxitin (88 percent and 92 percent, respectively). The difference in median increase in oral body temperature before and after the study (2.5 degrees F for cefotetan and 2 degrees F for cefoxitin) was statistically but not clinically significant (p = 0.03). Although nearly four times as many cefotetan patients as cefoxitin patients had surgery lasting 4 hours or more, the satisfactory bacteriologic response rates for cefotetan and cefoxitin were similar (88 percent and 93 percent, respectively). Nonobese patients and patients whose surgical procedures lasted less than 4 hours treated with either drug had significantly higher success rates (p less than 0.01). The incidence of major wound infection was approximately 8 percent for both treatment groups. Mean concentrations of cefotetan in plasma, specimens of colon, and subcutaneous fat were 128 +/- 61.8 micrograms/ml, 57.2 +/- 40.4 micrograms/g, and 26.8 +/- 19.4 micrograms/g, respectively. The incidence of adverse reactions was 12 percent for each group, and no reaction was considered treatment-related, including changes in results of clinical laboratory tests. A single 2 g preoperative dose of cefotetan was as safe and effective as multiple doses of cefoxitin in the reduction of postoperative wound infections after colorectal surgery.