Alterations in transcription factors NF-kB, CREB, AP1, SP1, GRE and OCT1 binding to specific known promoter DNA consensus sequences of immune cells from irradiated and shamirradiated mice 4 hours after whole body irradiation (WBI) with 75 mGy X-rays were investigated with gel mobility shift assay. Increased binding to NF-kB and CREB consensus sequence was found with nuclear extracts prepared from thymocytes and splenocytes of irradiated versus sham-irradiated mice. Protein binding to the NF-kB consensus sequence by nuclear extracts derived from irradiated mice was 5-fold in splenocytes and 4.3-fold in thymocytes higher than that from sham-irradiated. Competition with the cold oligonucleotide containing the consensus suquence for NF-kB resulted in loss of the shifed band at 25-fold excess concentration,indicating specific binding. DNA mobility shift assay using CREB consensus sequence showed 7-fold increace in splenocytes and 6-fold increase in thymocytes after low dose radiation (LDR) . Competition assays using cold oligonucleotide containing the CREB site eliminated the shift band at 50-fold excess concentration. The binding of AP1 consensus sequence showed a 2-fold increase in thymocyte nuclear extracts after LDR. No changes in protein binding to SP1, GRE and OCT1 consensus sequences were noted. The results indicate that activation of selective transcription factors NF-kB,CREB and AP1 of the immune cells in mice occurred after LDR.