The mouse late 2-cell embryos were cultured in control media(Ham's F-10 +10%FBS), media with Vero cell monolayer and Vero cell-conditioned media for 4 days and measured the hatching rate and cell number in the blastocyst stage.

The hatching rate in experimental groups was increased significantly compared with embryos in control group(p<0.01). On the other hand, the degree of blastomere fragmentaion exhibited a opposite trend to that of the developmental capacity(p<0.05). And also the cell numbers of expanded blastocysts in experimental groups were increased significantly compared with the control group(p<0.001). There was, however, no difference between experimental groups.

These results indicate that Vero cell-conditioned medium supported the mouse embryo development as a Vero cell monolayer. And the mechanism for enhancement of the development potential of embryos may be releasing the embryotrophic factor during the medium-conditioning period.