The mechanism of development of mouse fertilized eggs from the one-cell stage to the two-cell stage remains unclear to date. In the present study, we have evaluated protein kinase C (PKC) and M-phase promoting factor (MPF) kinase activity in fertilized mouse eggs treated with a PKC modulator. PKC and MPF activity have similar activity. The two subunits of MPF, p34(cdc2) and cyclin B, were shown to be included in the substrates phosphorylated by PKC in fertilized mouse eggs, while PKC modulator affected the electrophoretic mobility shift of cdc2 and cdc25C by dephosphorylation and phosphorylation. These results clearly indicate that PKC may affect the progression of the cell cycle through post-translational modification of MPF activity.