C57BL/6J mice implanted with Lewis lung carcinoma cells in the right thighs were used as an experimental animal model and whole body irradiation (WBI) with 75mGy X-rays was given at the 10th day after tumor implantation. We detected the cytostasis function of peritoneal Mϕ of the mice (with the method of ,3,H-TdR incorporation assay) and the levels of TNFα and IL-1β mRNA transcription (with the method of in situ hybridization immunohistochemistry) 18 hours after irradiation. The experiment showed that the cytostasis function of peritoneal Mϕ of irradiated mice was significantly increased compared with that of the sham-irradiated mice (irradiated mice: 79.9±4.2%, sham-irradiated mice: 52.9±8.1%,p,<,0.01). The levels of TNFα and IL-1β mRNA transcription were quantitatively measured with a scanning densitometry and the data showed that both the TNFα and IL-1β mRNA transcriptional levels of peritoneal Mϕ of irradiated mice were much higher than those of sham-irradiated mice (,p,<,0.01). The results mentioned above suggested that low dose radiation could markedly enhance the Mϕ function in tumor-bearing mice and the enhanced Mϕ function played an important role in the process of immunoenhancement and antitumor immune reaction induced by low dose radiation.