The activity of pyruvate dehydrogenase (PDH) increases during the oocyte maturation in the loach Misgurnus fossilis due, apparently, to the decrease of pyruvate utilization in the reactions of gluconeogenesis. The activity of PDH decreases twice at the stage of gastrula. These changes in the PDH activity are not related to intertconversion of the enzyme active and inactive forms of PDH; the total PDH of oocytes and embryos is in the active form only.