It has been shown that mouse ovarian follicles have a large glycolytic capacity, and this study was undertaken to determine whether follicles can develop normally using glycolysis alone. Pre-antral mouse follicles were grown using an in-vitro system which supports development to the preovulatory stage within 5 days. Cultures were maintained in either aerobic conditions in the presence of the inhibitor of oxidative phosphorylation, sodium malonate, or under anaerobic conditions. Samples of media were removed every 24 h and analysed for oestradiol using an enzyme-linked immunosorbent assay (ELISA) technique and for lactate and glucose using a fluorometric assay. Follicle size, oestradiol production and glycolytic rate were not significantly different between control and sodium malonate-treated follicles. Follicles cultured under anaerobic conditions showed significantly slower rates of growth and oestradiol production compared with controls. However, the rate of glycolysis was significantly higher during anoxia. Results indicated that anaerobic glycolysis may sustain limited periods of growth during the pre-antral phase, but that the presence of oxygen is vital to ensure normal development. It is concluded that pre-antral follicles can undergo development to the preovulatory stage using glycolysis alone, a feature which may allow them to conserve their limited supply of oxygen for other vital biosynthetic processes.