The meiotic cell cycle in mammalian oocytes commences in the fetal ovary, proceeds up to the diplotene stage of the first prophase, and is arrested around birth at a G2-like phase. Reinitiation of meiosis, which occurs immediately before ovulation, represents the transition from G2 to M phase of the cell cycle. Resumption of meiosis is associated with a reduction in cAMP concentrations within the oocyte and is negatively regulated by an activated cAMP-dependent protein kinase (PKA). These findings led to the hypothesis that meiotic arrest is mediated by a PKA-phosphoprotein substrate, which undergoes dephosphorylation under conditions of decreasing intra-oocyte concentrations of cAMP. Thus far, a phosphoprotein that serves as a substrate for PKA and maintains meiotic arrest has not been identified. Nevertheless, the idea that regulation of enzyme activities of a series of protein kinases and phosphatases governs the progression through the meiotic cell cycle is now commonly accepted. The present knowledge of the specific phosphorylation/dephosphorylation biochemical events that participate in the control of meiosis in mammalian oocytes is discussed in this review.