In order to investigate the effects of interleukin-18 (IL-18) on airway inflammation and the Th1/Th2 cytokine balance in guinea pig asthmatic model as well as its possible mechanisms, the asthmatic model was established by intraperitoneal injection of ovalbumin (OVA) and aerosol challenges into guinea pigs, and 30 treated animals were randomly divided into three groups of 10 animals in each groups, in which group A served as the asthmatic model, group B as the controls and group C as the group treated with IL-18. The counting and categorization of the inflammatory cells in bronchoalveolar lavage fluid (BALF) were performed by using light microscopy, and the contents of cytokines (IFN-γ, IL-2, IL-4 and IL-5) were assayed by means of the ELISA kit. The experimental results showed that the numbers of eosinophils (ESO) in BALF of group A, B and C were (97.70±58.03)×10~6/L, (11.68±9.95)×10~6/L and (28.62±10.46)×10~6/L, respectively, in which the number of eosinophils in group A was significantly higher than those of group B and C. Also, the number of neutrophils in BALF of group A was even higher than those in group B and C. In addition, the contents of IFN-γ and IL-2 in group A were lower than those in group B and C, but the contents of IL-4 as well as IL-5 were rather higher than those in group B and C. It is evident from the above observations that IL-18 can effectively inhibit the asthmatic inflammatory cells in BALF with an imbalance of the Th1/Th2 cytokines, thus offering the experimental basis for the clinical application of IL-18 in the prevention and treatment of asthma. In order to investigate the effects of interleukin-18 (IL-18) on airway inflammation and the Th1 / Th2 cytokine balance in guinea pig asthmatic model as well as its possible mechanisms, the asthmatic model was established by intraperitoneal injection of ovalbumin (OVA) and aerosol challenges into guinea pigs, and 30 treated animals were randomly divided into three groups of 10 animals in each groups, in which group A served as the asthmatic model, group B as the controls and group C as the group treated with IL-18 . The counting and categorization of the inflammatory cells in bronchoalveolar lavage fluid (BALF) were performed by using light microscopy, and the contents of cytokines (IFN-γ, IL-2, IL-4 and IL-5) were assayed by means of the ELISA results showed that the numbers of eosinophils (ESO) in BALF of group A, B and C were (97.70 ± 58.03) × 10 ~ 6 / L, (11.68 ± 9.95) × 10 ~ 6 / L and (28.62 ± 10.46) × 10 ~ 6 / L, respectively, in which the number of eosinophils in group A was s ignificantly higher than those of group B and C. Also, the number of neutrophils in BALF of group A was even higher than those in group B and C. In addition, the contents of IFN-γ and IL-2 in group A were lower than those in group B and C, but the contents of IL-4 were well higher than those in group B and C. It is evident from the above observations that IL-18 can effectively inhibit the asthmatic inflammatory cells in BALF with an imbalance of the Th1 / Th2 cytokines, thus offering the experimental basis for the clinical application of IL-18 in the prevention and treatment of asthma.