Using adult rabbits, the author performed the bone-marrow tissue cultures in fluid medium from the rabbits irradiated repeatedly and systemically with 100r of X-ray irradiation, 24-42 times; 300r, 10 times; and 1,000r once only and observed for the periods of 1-30 days; and obtained the following results. 1) In the group repeatedly irradiated wiht 100r X-ray, both the rate of increase of erythrocyte count as well as that of hemoglobin count decreased markedly. 2) In the group subjected to the irradiation of 3000r, the rate of erythrocyte count and that of hemoglobin count likewise decreased markedly. 3) In the group receiving a single irradiation of 1,000r, the rate of erythrocyte count and that of hemoglbin count decreased gradually along with the lapse of time, and both values reached their minimum on the tenth day while by the thirtieth day both were found to be at the normal. 4) In the repeated irradiations as mentioned above, the erythropoietic function is disturbed in parallel with the function of hemoglobin synthesis, whereas in the group subjected to a single irraiation of 1,000r X-ray, the erythropoietic function seems to be affected more markedly than the function of hemoglbin synthesis. Therefore, in the case receiving smaller doses it is assumed that the erythropoietic function is affected prior to the function of hemoglobin synthesis.