Objective:To investigate the alteration of peripheral blood interleukin(IL)-4,IL-9,and IL-21 in patients with bronchial asthma. Methods:Forty-eight asthma patients in acute stage,41 patients in remission stage,and 48 sex and age paired healthy controls were enrolled in this study. The expression of IL-4,IL-9,and IL-21 from serum and peripheral blood mononuclear cells were analyzed by ELISA and real-time PCR. And the value of FEV1% and the expression level of serum IgE were detected by allergy method and ELISA respectively. Results:①The mRNA and protein expression levels of IL-4,IL-9,and IL-21 were significantly increased in acute asthma patients compared with patients in remission group (P < 0.05 or P < 0.01). Also the mRNA and protein expression levels of IL-4 and IL-9 were significantly higher in remission group than that of control group (P < 0.05 or P < 0.01). But there was no significant difference in the mRNA and protein expression levels of IL-21 between remission group and control group (P > 0.05). ②In asthma patients,no correlation was found among the serum concentration of IL-4,IL-9 and IL-21,except of correlation between IL-9 and IL-4. The serum levels of IL-4 and IL-9 from asthma patients were positively correlated with the serum level of total IgE (P < 0.05) but negatively correlated with FEV1% (P < 0.05). But no obvious correlation was found between the serum concentration of IL-21 and the serum level of total IgE or FEV1% (P > 0.05). Conclusion:IL-4,IL-9,and IL-21 may play important roles in the pathogenesis of bronchial asthma. IL-4 and IL-9 monitoring allows for an assessment of the asthma status which is helpful to guide clinical treatment.