The effect of a preoperative single intravenous dose of metronidazole was studied in a prospective trial of 203 patients. 17.5% of the patients in the control group developed a wound infection compared with 3.4% of those receiving metronidazole (p less than 0.001). The average length of hospitalization and convalescence was significantly reduced in the metronidazole group. The use of metronidazole in prevention of wound infection is recommended.