The possibility that radiation-induced alterations in gene expression are tissue specific and are related to apoptosis was examined using samples from brain, heart, lung, spleen and intestine from female C57BL6 mice after exposure to 0.2 Gy radiation. Apoptosis was the highest in spleen and intestine, moderate in lung, and absent in brain and heart. However, the mRNA expression of Trp53 and Cdkn1a (p21) after irradiation was not different among the organ types, and immunohistochemistry revealed that all the organs expressed these two proteins after irradiation. When expression patterns of 23 genes in the organs were examined by RT-PCR, neogenine, Apo1, nuclease sensitive element binding protein 1, syntaxin, cyclin G1, hNOP56, paraoxonase and glutathione peroxidase were overexpressed after irradiation in all the organs sampled, suggesting them as universal exposure markers for low-dose radiation. Sialyltransferase may be a candidate for radiation detection in spleen and intestine, which are radiosensitive organs. Because Sod1 (Cu/ZnSOD) and alphaB crystalline were expressed only in spleen, and protein tyrosine kinase and platelet membrane glycoprotein lib were expressed in both spleen and lung, these genes may also be potential markers for detection of radiation exposure, especially low-dose radiation, in these tissues. These data suggested possible tissue-specific markers of low-dose radiation exposure and suggested potential novel genetic modifiers of radiation response.