[en] In order to explore the influence of dose rate on radiation hormesis after low dose irradiation, Balb/c mice were irradiated at a same total dose with dose rates of 12.7 mGy/min and 0.2 Gy/min. The results showed that different biological effects were induced by different dose rates at the same dose. The response of splenic lymphocytes to Con A assessed by ³H-TdR incorporation was increased after irradiation with a dose rate of 12.7 mGy/min, which is especially marked following total doses of 76.7 mGy and 105.5 mGy (P<0.01). However, the response of splenic lymphocytes to Con A showed no significant changes after irradiation with a dose rate of 0.2 mGy/min at the same total dose. The result indicated that low dose radiation hormesis could not be induced by high dose rate X-rays