The level of kinase activity of cdkl is known to be high during metaphase of the two meioses. In this experiment, histone H1 kinase activity (which is known to reflect cdk1 activity) was assayed in BALB/c mouse ovulated oocytes at various timepoints after ovulation. Histone H1 kinase activity in ovulated oocytes was stable up to 37 hours after ovulation. After that time, histone H1 kinase activity significantly decreased suggesting that cdkl might be degraded after this period of time if the ovulated oocyte is not fertilised.