In an effort to determine whether or not the addition of parenteral antibiotics to orally administered erythromycin and neomycin would diminish postoperative septic complications in elective colorectal operations, a randomized, double-blind, controlled trial was conducted comparing three groups. All patients received vigorous preoperative mechanical bowel preparation, 3 g erythromycin and 3 g neomycin orally, the day prior to operation. Patients in Group O received three doses of saline intravenously as placebo, patients in Group C received cefazolin, 1 g, immediately preoperatively and 1 g every 6 hours postoperatively, intravenously, for two doses, and patients in Group T received a single immediate preoperative dose of 6 g of ticarcillin intravenously and two saline placebo doses intravenously, postoperatively. The patients' progress was followed in the hospital and for one month postoperatively. Septic complications occurred in 35 per cent of patients in Group O, 7 per cent of patients in Group C, and 5 per cent of patients in Group T. Wound infections comprised most of these complications, occurring in 29 per cent of Group O, 4.7 per cent of Group C, and 2.3 per cent of Group T patients. Thus, the addition of either parenteral cefazolin or ticarcillin in this study significantly reduced wound infections in elective colorectal surgery.