Some new findings regarded the dynamics of the changes in the white component of peripheral blood, particularly at early intervals in the case of three clinically differing doses of ionizing radiation were obtained. At the highest dose early nonspecific leucocytosis was recorded only six hours after the exposure. Significant neutrophili occurred in the case of all three doses beginning from the sixth hour. With the highest dose it had the shortest duration and highest values, and at the smallest dose the opposite was the case. In the case of the highest dose leucopenia sets in after 24 hours, and in the case of the other doses not until after 36 hours. Lymphopenia appears already after 6 hours, the consequences according to the doses, however, manifest themselves only after 12 hours. In all three groups leucopenia and lymphopenia have a constant character. It was confirmed that the changes in the white blood component were the most typical response to the exposure to ionizing radiation, and orientation and special criteria have been found for the estimation of the consequences of the forms of irradiation on the basis of numerical changes of leucocytes, lymphocytes, and neutrophilic granulocytes within 72 hours after the exposure.