The aim of our study was to evaluate the frequency of Chlamydia pneumoniae infection (especially chronic infection) in 41 asthma patients. They have been assigned to 3 groups, according to disease severity. Control group consisted of 35 age matched healthy volunteers (without cardiac and pulmonary diseases). The levels of specific IgG, IgA and IgM in patients' serum have been estimated using indirect microimmunofluorescence. According to serologic criteria, 23(56.1%) asthma patients and 4(11.4%) healthy controls have appeared to be chronically infected with Chlamydia pneumoniae (p < 0.001). Acute Chlamydia pneumoniae infection was present in 3(7.3%) asthma patients and in 2(5.7%) healthy controls. Taking in account asthma severity, persistent Chlamydia pneumoniae infection has occurred more frequently in patients with moderate and severe asthma than in ones with mild asthma. Acute Chlamydia pneumoniae infection was present in 9.1% and 12.5% of patients with mild and severe asthma respectively.