We investigated preoperative PaO2 and changes of PaO2/FIO2 (P/F) during the operation in 40 patients with gynecologic malignancies (ovarian cancer (O group) = 14 cases, endometrial cancer (E group) = 14 cases, cervical cancer (C group) = 12 cases). Preoperative chest X-ray and respiratory function test of our patients were within normal ranges (% VC > or = 80, % FEV 1.0 > or = 70). There were no differences among 3 groups in age, height, weight, % VC, or % FEV 1.0. Preoperative PaO2 values in the O group and E group were significantly lower than the normal value (100--age/4). Preoperative PaO2 and P/F values in the O group were significantly lower in comparison with those in the C group. We suggest, therefore, that it is necessary to measure preoperative PaO2 in patients with ovarian and endometrial cancer.