The experiments reported here take advantage of the large number of in vitro matured and in vitro fertilized(IVM /IVF) bovine oocytes which can be produced, permitting the design of controlled experiments to establish a simple defined medium for the study of early embryo requirements. A total of 1,386 IVM /IVF oocytes were used to compare a simple defined medium(KSOM) with more complex culture conditions used successfully for culture of bovine embryos but do not permit study of specific requirements. All experiments were extensively replicated factorials. In Experiment 1, KSOM was superior to Menezo B$_2$ medium in producing morulae plus blastocysts from IVM /IVF oocytes(33 vs 20%, P<0.()5). The yield of morulae plus blastocysts with KSOM was 22% and with BRLC added was 30%. In Experiment 2, (a 2x2 factorial of KSOM with or without BRLC and 0, 1 ng /ml of platelet derived growth factor, PDGF) more morulae plus blastocysts (40%) were produced in KSOM-BRLC co-culture containing 1 ng /ml PDGF than in the control KSOM(12%). In Experiment 3, there was no dose response when 0, 1 and 5 ng /ml of PDGF were added. The results with simple defined KSOM medium are sufficiently promising to indicate that specific requirements of the embryo may be examined in future studies with KSOM as a base.