This study was aimed to investigate the expression and clinical significance of IL-18, IL-18 binding protein (IL-18BP), IFN-γ and IL-4 secreted from splenocytes of patients with idiopathic thrombocytopenic purpura (ITP) in vitro. Spleen mononuclear cells (MNC) were prepared by using routine sterile method, and were cultured in RPMI 1640 complete medium containing 10 µg/ml PHA, 10% fetal calf serum at 37°C and 5% CO2. The levels of IFN-γ, IL-4, IL-18 and IL-18BP secreted from MNC of ITP patients and normal controls were determined after culture for 48 hours. The results showed that after culture of spleen MNC for 48 hours, the levels of IL-18 and IFN-γ were significantly higher in patients with ITP than that in controls, but the levels of IL-18BP was not significantly elevated in ITP patients. The level of IL-4 was below the detectable limit of the assay used. It is concluded that imbalance between IL-18 and IL-18BP may play an important role in pathogenesis of ITP, and regulation of balance between IL-18 and IL-18BP may be a therapeutic approach against ITP.