The change in hemograms of mice was investigated after a whole-body bose of 300R of x-rays. Cepharanthin, a biscoclaurine alkaloid, was injected intraperitoneally 0.1, 0.2 and 0.4mg per mouse into mice from the first day to the fourteenth day following the irradiation. Cepharanthin (0.1mg) significantly accelerated the recovery of peripheral leukocytes compared with the control. However, cepharanthin injected at higher concentrations was less effective, thus the optimum dose was 0.1mg. In a differntial count of leukocytes, the relative percentage of granulocytes decreased in control irradiated mice, and increased in cepharanthin injected mice. The difference in the recovery of the actual number of lymphocytes was not statistically significant between the control and cephalanthin injected mice. This fact indicates that the marked recovery of leukocytes after irradiation followed by cepharanthin is due to the increased the recovery of actual number of granulocytes. The effect of cepharanthin was discussed in relation to radiation damage of hemopoietic function.