The course of 200 patients who recently underwent appendectomy at UCLA for acute appendicitis has been reviewed to determine the efficacy of preoperative systemic antibiotic prophylaxis in reducing septic morbidity after surgery. Among those with nonperforated appendicitis who were given gentamycin and clindamycin preoperatively, a reduction of infection rate from 10.2 to 5.3 per cent was found when compared with patients who received no antibiotics.