Introduction. Gynecologic laparoscopic surgery has high incidence of postoperative nausea/vomiting (PONV) up to 80% without prophylaxis (1). Whether high inspired oxygen fraction (FIO2) 0.8 reduces the incidence of PONV in gynecologic laparoscopy is controversial (2, 3). We investigated whether different intraoperative oxygen (O2) fractions reduce PONV in gynecologic laparoscopy. Methods. After obtaining IRB approval, 108 women ASA PS I-II, 21-75 years old, scheduled for gynecological laparoscopic surgery were randomized into three groups: G30 = 30% O2 in air (n=36), G50 = 50% O2 in air (n=36) and G80 = 80% O2 in air (n=36). Patients received 7.5 mg of midazolam PO 1h preop. No PONV prophylaxis was given. Anesthesia was induced with thiopental 5 mg/kg, vecuronium 0.1 mg/kg and fentanyl 1-2 g/kg, followed by 10 mL/kg/h saline and maintained with sevoflurane 1MAC. Patients were considered to have had PONV if at least one episode of nausea, vomiting or retching or any combination of these occurred during 24h postop. PONV and pain was assessed at 2h and 24h after surgery. Diclofenac IM and pethidine IV were used for postop pain and metoclopramide IV for PONV. Data were expressed as mean SD and analyzed using and Kruskal-Wallis test. P