Mycobacteria are the strong stimulators of respiratory burst, resulting in production of reactive oxygen species and nitrogen intermediates. The aim of our study was to assess the concentration of hydrogen peroxide (H(2)O(2)) in expired breath condensate (EBC) and the serum level of interleukin-18 (IL-18) in patients with active pulmonary tuberculosis (TB) before introduction of chemotherapy and after 2 months of treatment. Sixteen patients, current cigarette smokers, with advanced pulmonary TB were enrolled into the study. As a control served two groups: I group--16 asymptomatic cigarette smokers, II group--17 healthy never smoked subjects. The level of H(2)O(2) in EBC was significantly higher in patients with TB (1.3+/-0.7 microM) as compared to cigarette are healthy nonsmoker subjects (0.4+/-0.1 and 0.2+/-0.1 microM, respectively, P<0.05). Two months of treatment significantly decreased the level of H(2)O(2) exhalation in TB patients (0.5+/-0.3 microM) to the value that was not different from that in asymptomatic smokers but was still higher than in never smoked subjects. Serum concentration of IL-18 in TB patients was higher than that found in both control groups either before and after antituberculous treatment (P<0.05). Exhaled H(2)O(2) did not correlate with circulating IL-18 in TB patients before or after treatment. These results demonstrated the occurrence of oxidative stress in the airways of TB patients completely attenuating after 2 months of successful antituberculous treatment.