The objective was to observe the effects of 0.075 Gy low dose radiation (LDR) on the synthesis of IL-10 in splenocytes and the secretion of IL-12 by peritoneal macrophages. Kunming mice were selected and randomly grouped. Northern blot and flow cytometry were adopted to detect the changes of IL-10 at mRNA and protein levels, respectively. Northern blot and ELISA were used, respectively, to examine the changes of IL-12 p35/p40 mRNA and IL-12 p70 protein levels. IL-10 mRNA decreased significantly in splenocytes, while both IL-12 p35 and p40 subunit mRNA levels in macrophages increased after whole body irradiation (WBI) with 0.075 Gy x-rays. Meanwhile, IL-10 synthesis in splenocytes decreased beginning from 4 h after exposure and remaining at a lower level up to 48 h, and IL-12 secretion by macrophages was found to take the opposite direction, i.e. increase significantly. In conclusion, WBI with 0.075 Gy x-rays may suppress IL-10 both at the mRNA level and protein level and stimulate IL-12 expression simultaneously, which might contribute to a shift of the immune response in favour of Th1 differentiation.