To explore the effect of ionizing radiation on the expression of metallothionein (MT) in immune organs, the ,109,Cd-hamoglobulin affinity assay was employed to measure the content of MT in tissues. The dose effect relationship of the MT expression in mouse thymus and spleen was investigated 16h after exposure to 0.5, 1, 2, 4 and 6Gy whole body irradiation(WBI). And the time course changes in MT expression in mouse thymus and spleen were also determined at different time intervals after 4Gy WBI. The results showed that the MT content in mouse thymus was significantly increased 16h after 4Gy and 6Gy irradiation compared with that in sham-irradiated mice (p ,<,0.05, respectively). And it was found that the MT content in mouse thymus was also increased significantly from 8h to 48h after 4Gy irradiation compared with that in sham-irradiated mice (,p,<, 0.05 ~,p,<,0.001). However, there were no markedly changes for the MT expression in the mouse spleen after exposure to X rays. These results mentioned above suggest that the MT expression in immune organs could be induced by X rays, which may be tissue-specific.