Unfertilized eggs of the sea urchin, Hemicentrotus pulcherrimus, were irradiated with 60Co γ-rays. Incorporation of 14C-leucine into the protein fraction increased after 25 krads of irradiation. A slight acceleration of glycolysis by irradiation was indicated by the measurement of glycolytic intermediates both in unfertilized and fertilized eggs. However, the degree of activation of glycolysis with irradiation was much less than that follows fertilization. However, the abnormal accumulation of fructose diphosphate after irradiation, which has been observed in tumor cells or thymocytes, was not observed in the eggs and was discussed in relation to cellular radiosensitivity.