Fertilization-induced Ca² oscillations in mouse eggs cease at the time of pronuclear formation when maturation-promoting factor (MPF) is inactivated, but the Ca² oscillations are ceaseless if eggs are arrested at metaphase by colcemid, which maintains the activity of MPF. To determine the possible role of MPF in regulation of cytoplasmic Ca² excitability, roscovitine, a specific inhibitor of p34^cdc2/cyclin B kinase, was used to inactivate MPF, and its effect on fertilization-induced Ca² oscillations was investigated. Our results showed that roscovitine at ≥ 50 μM suppressed fertilization-induced Ca² oscillations in normal and colcemid-treated metaphase II (MII) eggs after the first 1–2 Ca² spikes. Roscovitine inhibition of fertilization-induced Ca² oscillations could be reversed by extensive washing of the eggs. Histone H1 kinase activity in colcemid-treated MII eggs was similarly inhibited by roscovitine, which suggested that the cessation of fertilization-induced Ca² oscillations is due to the inactivation of MPF. Thimerosal-induced Ca² oscillations in Ca² -, Mg² -free medium was also suppressed by roscovitine, suggesting a general inhibitory effect of roscovitine on Ca² oscillations. The inhibition may be achieved by disruption of Ca² release and refilling of the calcium store. Thapsigargin, an inhibitor of the endoplasmic reticulum Ca-ATPase, induced significantly less Ca² release in roscovitine-treated eggs than in the non-drug-treated eggs. Taken together, our results suggest that MPF plays an important role in regulation of the cytoplasmic Ca² excitability in mouse eggs.