['Obtaining mature human follicles from cultured ovarian tissue may be beneficial for clinical use for women who wish to preserve fertile competence. However, the methodology of culture such as culture condition and gas atmosphere has not been well established in humans. Therefore, we investigated the effect of oxygen concentration in organ culture in order to establish an ovarian tissue culture method.', 'Ovarian tissue was obtained from 26-35-year-old women undergoing removal of a benign tumor (n = 12) or caesarean section (n = 16). The ovarian cortical tissues were cultured on a cell culture insert for 15 days under high (100%) and low (air, 20%) oxygen concentrations and then inspected for follicle development with light and electron microscopy. Estradiol and progesterone concentrations in the medium during culture were measured.', 'The ultrastructure and the function of hormone secretion in the cultured tissues were well preserved after organ culture. The follicles developing under high oxygen were larger and more matured than those developing under low oxygen (P < 0.05).'] Does high oxygen atmosphere improve human follicle development in organ cultures of ovarian cortical tissues in vitro?