A total of 110 patients undergoing elective abdominal hysterectomy were anesthetized in random order with either isoflurane in nitrous oxide and oxygen or isoflurane in air and oxygen. Fentanyl was used as an adjunct to isoflurane in all patients, 0.05 mg every 45 min. No difference was found between the two anesthetic techniques in the incidence of nausea, vomiting, or both during the first 24 hr after operation. The overall incidence was 62 and 67% for air-O2 and N2O-O2 groups, respectively. Patients who had had nausea or vomiting after previous anesthetics had nausea or vomiting significantly more frequently than patients who did not. It is concluded that nitrous oxide does not contribute to the occurrence of nausea or vomiting after isoflurane anesthesia for gynecologic laparotomies.