Objective: Immature mammalian oocytes cultured in vitro undergo inadequate cytoplasmic maturation and hence have a limited potential for fertilization. Our primary objective was to determine if the addition of epidermal growth factor (EGF) to the in vitro culture system would have a positive effect on oocyte cytoplasmic maturation. Design: We studied the effect of different EGF concentrations on both denuded and cumulus-enclosed mouse oocytes cultured in vitro. Main Outcome Measures: The percentage of oocytes undergoing germinal vesicle breakdown (GVBD) and polar body one formation over time as a function of EGF concentration was determined. Results: A dose-related positive effect of EGF on both GVBD and polar body one formation over time was observed for mouse oocytes. As well, a similar effect of EGF was seen on immature human oocytes that had not been stimulated with exogenous gonadotropins. Conclusions: The use of EGF may allow for the performance of successful in vitro fertilization procedures using immature human oocytes retrieved during unstimulated cycles.