[en] Objective: To observe the effect of X-rays irradiation on IL-18 expression in mouse peritoneal macrophages. Methods: Eiyghty Kunming white mice were divided into 10 groups (eight each group): sham-irradiation, four groups of low-dose irradiation (0.05, 0.075, 0.1 and 0.2 Gy), and five groups of high-dose irradiation (0.5, 1.0, 2.0, 4.0 and 6.0 Gy). The mice were killed 16 h after whole body irradiation (WBI), with X-rays then the peritoneal macrophages were obtained and cultivated with culture medium of RPMI 1640 in culture box with 37 degree C, 5% CO₂ for 72 h. The supernate was gathered to detect the IL-18 expression level in macrophages by ELISA. Results: The IL-18 expresson level in sham-irradiation group was (51.29±3.26) ng·L^-1, IL-18 expression was enhanced after 0.05 Gy WBI, but there was no significant difference (P>0.05). The expression level was increased to (122.78±8.07) ng·L^-1 after 0.075 Gy WBI, and there was significant difference compared with sham-irridiation group (P<0.01). IL-18 expression was increased gradually with the enhancement of X-rays irradiated doses (0.1, 0.2, 0.5 and 1.0 Gy), and the values were (135.32±5.27), (149.40±16.54), (200.42 ± 15.42) and (347.59 ± 17.88) ng·L^-'1, respectively. It peaked after 1.0 Gy irradiation, then it decreased after 2.0, 4.0 and 6.0 Gy irradiation, and the values were (229.49±14.68), (253.79±6.69) and (223.32±20.85) ng·L^-1, respectively, but they were higher than that in sham-irradiation group (P<0.01). Conclusion: Both high-dose and low-dose X-rays irradiation can stimulate IL-18 expression in mouse peritoneal macrophages. (authors)