[en] The work is to observe whether human blood samples irradiated in vitro to 10 cGy by X-rays could be an incentive to normal blood samples and blood cells injured by high dose radiation (1000 cGy). The irradiated blood samples were cultured with blood samples collected from the same person, which were irradiated to 1000 cGy or without irradiation. The cpm of ³H-TdR incorporation in different groups was measured after 72-hour culturing. Experiment results suggested that the blood irradiated to 10 cGy could stimulate the blood cells irradiated to 1000 kGy to proliferate. There is something in the plasma resulting in the stimulating effect. (authors)