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