To observe the effects of LDR on the synthesis of IL—10 in splenocytes and the secretion of IL—12 by peritoneal macrophages. Northern blot and flow cytometry were adopted to detect the changes of IL—10 at mRNA and protein level, respectively. Northern blot and ELISA were used respectively to examine the changes of IL—12p35/p40 mRNA and IL—12p70 protein levels. In splenocytes IL—10 mRNA decreased significantly,while both IL—12 p35 and p40 subunits in macrophages increased after WBI with 75 mGy X rays. Meanwhile, IL—10 synthesis in splenocytes decreased beginning from 4h after exposure and remaining at low level up to 48h, and IL—12 secretion by macrophages was found to take an opposite direction. WBI with 75mGy X rays may suppress IL—10 both at the mRNA level and protein level and stimulate IL—12 expression simultaneously, and this would lead to a shift of the immune response in favour of T,H,1 differentiation.