Acute respiratory tract infections may trigger acute asthma attacks and may be held responsible for etiopathogenesis in children with asthma. Although bacterial infections attract a limited amount of attention, recently Chlamydia pneumoniae (CP) and Mycoplasma pneumoniae (MP), in particular, are reported to be the possible factors. IgM and IgG seroprevalence was investigated in 66 children patients with bronchial asthma (between the ages of 3 and 14) for CP and Mycoplasma pneumoniae. In a total of 66 cases, 18 (27.2%) patients were detected with IgG positivity for CP whereas 27 of them (40.9%) were detected with IgG positivity for MP. IgG positivity was determined in 6 patients (13.0%) in the control group for CP, and in 6 patients (10.8%) in the control group for MP. The rate of the asthma patients with IgG seropositivity for MP was 4 times higher than that of the control group. It was seen that IgG antibody seropositivity for CP was higher in those with more frequent attacks. No such difference was observed in terms of IgG antibody seropositivity for M. pneumoniae. There are many studies indicating that CP and MP infections take an importance place in the etiology of bronchial asthma and asthma attacks in children. The results obtained reveal the effect of both microorganisms on the etiopathogenesis of the bronchial asthma and the increased number of asthma attacks.