Higher proportions of oocytes matured in a defined medium with epidermal growth factor (EGF) and low concentrations of gonadotropins reached the blastocyst stage in vitro after in vitro fertilization than were obtained after in vitro maturation (IVM) in defined conditions alone, or with EGF and no gonadotropin. Proportions of cumulus-oocyte complexes undergoing partial and full cumulus expansion after IVM with 0, 1.0, 10.0, or 100 ng EGF/ml were 16.7%, 43.6%, 52.0%, and 63.0%, respectively; higher proportions also exhibited cumulus expansion after IVM with LH or FSH alone or in combination with EGF than after IVM in defined medium alone (p < 0.05). Varying concentrations of EGF in combination with low concentrations of either FSH or LH (0.5 micrograms/ml) for IVM increased the proportions (p < 0.05) of oocytes reaching the blastocyst stage over conditions afforded by each gonadotropin alone. For FSH+EGF at 1.0, 10.0, and 100 ng/ml, the proportions that reached the blastocyst stage were 33.7%, 39.5%, and 32.8%, respectively; for FSH alone, 13.0%. For LH+EGF at 10.0 and 100 ng/ml proportions were 33.3% and 30.8%, respectively; for LH alone, 15.3%. Combination of EGF with low concentrations of gonadotropins during IVM enabled subsequent blastocyst development in proportions comparable to those afforded by high concentrations of FSH or LH. Findings suggest a possible physiological role for EGF in regulating bovine oocyte maturation.