Chlamydophila pneumoniae was taxonomically separated from strain TWAR - an abbreviation of the strain isolated from humans TW-183 (material from the eye of a child in Taiwan in 1965) and AR-39 (material from a student's throat swab with acute changes within airways in Seattle in 1983). The basis of separation of the C. pneumoniae species was the unique structure of the elementary bodies. Infection caused by C. pneumoniae is often asymptomatic (60-80% of all infections). Symptomatic infections of the upper respiratory tract relate to pharyngitis, laryngitis, sinusitis and the lower respiratory tract: bronchitis and pneumonia. C. pneumoniae infection often transforms into a chronic, clinically oligo- or asymptomatic form. The chronic inflammatory process is associated by many authors with the pathogenesis of coronary artery disease, endocarditis, atherosclerosis, hypertension, vasculitis, multiple sclerosis, sarcoidosis, and asthma. C. pneumoniae has a specific tropism and exhibits cytotoxic activity towards the airway epithelium, in which it proliferates and destroys infected cells by lysis. Entry of these bacteria to the human body leads to activation of first non-specific and then specific resistance mechanisms and the development of a local inflammatory process. Diagnosis of C. pneumoniae should be confirmed only after the exclusion of typical micro-organisms causing respiratory infections. It is important to pay attention to the fact that the epidemiological data on the incidence of C. pneumoniae infections in different age groups of patients are variable depending on the type of diagnostic methods used in the research. Chlamydia are resistant to most antibiotics that are routinely used in respiratory tract infections. These bacteria are susceptible to antibiotics that disrupt the synthesis of DNA and proteins, such as macrolides, tetracyclines, and fluoroquinolones.