Objective　 To investigated the possible roles of IL-18 in HBV infection, and the expression of IL-18 in the peripheral blood mononuclear cells (PBMC) of chronic hepatitis B. Methods 　In 15 cases of asymptomatic carriers, 30 cases of active and remissive phases of chronic hepatitis and 10 healthy individuals (as normal controls), IL-18 expression in PBMC were quantitatively analyzed with flow cytometric immunological method. The PBMC were separated routinely and stimulated with LPS (SIGMA) and Monensin (SIGMA) for 6 hours. Then the cells were harvested and fixed by PBS/4% paraformaldehyde. The treated cells were stored in liquid nitrogen for detection later. After immunologic stain, the expression of IL-18 in PBMC were examined by flow cytometry. Results　 ① IL-18 was the lowest in asymptomatic carriers. It was fewer in remissive phase than in normal controls (P＜0.01).There was no difference between active phase and normal controls(P=0.25).②Within the group of active phase, IL-18 was significantly different between each grade of inflammatory activity(P＜0.01),and correlated with serum ALT positively(r=0.63,P＜0.01). Conclusion　 IL-18 may relate to disease activity and the inflammation of liver.