['This is the first study of the effect of epidermal growth factor (EGF) on marmoset monkey oocytes matured in vitro.', 'We have evaluated the effects of 10 ng/ml EGF in combination with 1 or 10 IU/ml of gonadotrophins (FSH/hCG 1:1 ratio) during in vitro maturation (IVM) of marmoset oocytes. Immature cumulus-oocyte complexes (COCs) were retrieved from ovarian antral follicles of unprimed monkeys. COCs from six animals (n= 268) used in this study were randomly distributed among four experimental groups: (A) 1 FSH +1 hCG; (B) 10 FSH +10 hCG; (C) 1 FSH +1 hCG + EGF; and (D) 10 FSH +10 hCG + EGF (where 1 and 10 are concentrations, IU/ml). After IVM, oocytes were fertilized in vitro and embryos were allowed to progress up to 87-88 h.', 'the highest rate of total and radial cumulus expansion was observed in Group A, with the lowest in Group B (P < 0.05). Neither maturation nor fertilization rate were affected by gonadotrophin concentration or presence of EGF. Addition of EGF increased degeneration and decreased first cleavage rate, which was significantly lower in Group C than Group A (P < 0.005). Interestingly, in the EGF groups some embryos cleaved faster than without EGF.'] Are epidermal growth factor effects on marmoset monkey ( Callithrix jacchus ) oocyte in vitro maturation , IVF and embryo development altered by gonadotrophin concentration during oocyte maturation?