The purpose of this research was to define the effects of various growth-promoting factors on in vitro embryonic development of in vitro matured and in vitro fertilized bovine embryos. The control medium was a chemically defined medium which improves the possibility of closely determining the in vivo conditions the embryo is actually exposed to. The growth-promoting factors tested in this experiment included transferrin, IGF-I (insulin-like growth factor-one), IGF-II (insulin-like growth factor-two), TGF-a (transforming growth factor-alpha) , TGF-B1 (transforming growth factor-beta1) , PDGF (platelet derived growth factor), EGF (epidermal growth factor), NGF (nerve growth factor), and bFGF (basic fibroblast growth factor). Transferrin was included at 10 micrograms/milliliter , while all other factors were utilized at 10 nanograms/milliliter in the control medium. Bovine cumulus-oocytes were retrieved from slaughterhouse ovaries and were matured i n Medium-199 containing 10% feta l bovine serum for 24 hours at 39°C in a 5% C02 atmosphere. Frozen-thawed bull spe r m were s wim-up separated and capacitated in medium containing heparin for 3 hours prior to insemination. Gametes were co- incubated fo r 18 hours and then cumulus cells were stripped from the ova. Ova which did not cleave were removed from culture 36 hours after insemi nati on and were stained for evidence of fertilization. Embryos were cultured in one of the 10 conditions (including control) described above. A total of 150 total oocy.t.es were cultured per treatment for a tota l of 10 days. EGF improved embryo development, while TGF-Bl and TGF-a only slightly improved embryo development compared to the control. All other factors tested did not have a beneficial effect on embryo development in this culture medium. In summary, EGF improved in vitro development of bovine embryos obtained from in vitro maturated and in vitro fertilized bovine oocytes. Other factors which were t est ed did not significantly improve in vitro bovine embryo development. Further experiments are necessary fo r determining the requirements of bovine embryos in vitro.