The aim of the study was to evaluate the effects of follicle stimulating hormone (FSH), luteinizing hormone (LH), epidermal growth factor (EGF) and estradiol 17-beta (E2) in maturation medium on nuclear maturation and cumulus expansion of cumulus-oocyte complexes (COCs) obtained from bovine ovaries. COCs were classified as good and poor quality grades based on cumulus investment. COCs were then subjected to in vitro maturation in TCM-199 in a humidified atmosphere of 5% CO(2) in air at 38.5 degrees C for a period of 24 h. The combination of the hormones added to the medium was as follows: T1=10% (v/v) heat inactivated Fetal Bovine Serum (FBS); T2=5 mu g/ml bLH, 0.5 mu g/ml bFSH and 10 ng/ml EGF; T3=FBS, bLH, bFSH and EGF; T4=1 mu g/ml E2; T5=FBS and E2. Supplementation of maturation medium with the FSH, LH, EGF irrespective to supplementation with FBS stimulated expansion of cumulus around the oocytes compared to oocytes in other treatment groups (P<0.05). However there were no significant differences between treatment groups in terms of proportion of oocytes reached to metaphase II (M II) stage determined by nuclear staining. In general cumulus expansion degree increased with the quality of COCs in all treatment groups (P<0.05). In conclusion, hormone and growth factor supplementation (FSH, LH and EGF) stimulated cumulus cell expansion and maturation rate.