Asthma is a chronic inflammatory airway disease characterized by variable airway obstruction and bronchial hyperresponsiveness. There are many factors affecting the development and severity of childhood asthma such as genetic predisposition, atopy, environmental factors, obesity, diet, socioeconomic status, and infectious triggers. In the present study we aimed to investigate the frequency of Mycdoplasma pneumoniae, Chlamydia pneumoniae, and Helicobacter pylori infections in asthmatic children. We investigated also whether there is a relationship between these agents and asthma attacks. METHODS Seventy-nine asthmatic children (46 males, aged 5-15 years) were included in study. The study group was divided into two groups: group 1 consisted of 37 children with asthma attacks and group 2 consisted of 42 children with stable asthma. As a control group we studied 36 healthy children. Pulmonary function tests, skin prick tests for common allergens were performed; serum total IgE, phadiatop, specific IgM and IgG antibody levels (ELISA) for M. pneumoniae, C. pneumoniae and H. pylori were measured in all patients. RESULTS Mycoplasma IgM and Chlamidia IgM were positive in 8.1% (3 patients) and 18.9% (7 patients) of group 1 patients, respectively. There was a statistically significant difference for Mycoplasma IgM (p = 0.031) and Chlamidia IgM (p = 0.03) between group1 and other two groups. We have not found significant difference for M. pneumoniae IgG, C. pneumoniae IgG and H. pylori IgM and IgG among groups. CONCLUSIONS M. Pneumoniae and C. Pneumoniae may play a role in development of asthma exacerbations in childhood. We could not find a relationship between H. Pylori and asthma.