Chlamydia pneumoniae is one of the most frequent pathogens causing airways infections. Contribution of chronic chlamydial infection to the following diseases: asthma, POChP, coronary heart disease, abdominal aortic aneurysm, is particularly interesting. The connection between such infection and bronchial asthma was described in the literature in 1991. C. pneumoniae often causes asthma exacerbation; it is suggested that it also may be an etiologic factor of the disease. In a group of 55 subjects with chronic, stable bronchial asthma treated in the Pulmonary Department, serologic characteristic of C. pneumoniae infection was found in 34 patients (61,8%). Thirteen of these subjects agreed to participate in the study. They were divided into two groups; placebo was administered to the first one and azithromycin in a dose of 1000 mg once a week--to the other one. The research was conducted using the double blind trial method. Anti-chlamydial antibody level was evaluated before and after treatment. Spirometry tests as well as subjective estimation of physical fitness and dyspnoea degree were also determined. In comparison with 'the placebo group', statistically significant improvement in respiratory parameters 'in the treated group' was not ascertained.