The effect of whole-body irradiation (WBI) on transcriptional regulation in mouse spleen was studied using gel electrophoresis mobility shift assay (EMSA) and oligonucleotide competitive inhibition analysis. Binding of nuclear protein extract from splenic cells to ［γ- ³²P］ ATP labeled CREB and NF-κB consensus sequences was found to be increased 4 h after WBI with 75 mGy X-rays, being 7 and 5 times higher, respectively, than that of the sham-irradiated control. Competitive inhibition analysis with excessive amount of unlabeled consensus sequences completely blocked the binding in corresponding EMSA, demonstrating the specificity of the reaction. The results suggest that low dose WBI could selectively activate the transcription factors CREB and NF-κB, which would induce specific gene transcription in the splenic cells leading to their functional activation.