The role of metronidazole in reducing the incidence of infectious complications after appendectomy has been established, but the value of an additional antibiotic to act against aerobic pathogens remains controversial. Patients who received 2 grams of cefotetan intravenously at the time of appendectomy and those who did not were compared for the incidence of infection. All patients received 1 gram of metronidazole per rectum preoperatively and every 12 hours for five days postoperatively. Infection occurred in three patients who received cefotetan and 16 of those who did not (p less than 0.01). We conclude that a single dose of cefotetan, an antibiotic which is effective against aerobic and anaerobic organisms, produces a significant reduction in the incidence of infection when added to metronidazole in the management of patients after appendectomy.