OBJECTIVE: To identify whether there is an association between an acute attack of childhood bronchial asthma and Chlamydia pneumoniae(CP) infection. METHODS: Serum specific antibodies IgM and IgG to CP were detected by ELISA in 120 asthmatic children with an acute attack and 82 healthy children. RESULTS: Anti-CP IgM was demonstrated in 22 cases(18.3%) and anti-CP IgG was demonstrated in 32 cases(26.7%) out of the 120 asthmatic patients.The incidence of CP infection in asthmatic children was significantly higher than that in healthy controls(3.7%)(P<0.01). Glucocorticoid inhalation treatment alone resulted in a remission of an acute attack of asthma in 15 cases out of the 32 cases with CP infection, but 17 cases required glucocorticoid inhalation treatment together with anti-CP infection treatment(macrolide antibiotics,eg.azithromycin) for remission of asthma attack. CONCLUSIONS: There may be a link between an acute attack of childhood asthma and CP infection.It is thus necessary to detect the CP-specific antibodies in asthmatic children for proper treatment.