Aim. To assess the role of matrix metalloproteinases (MMP) in the clinical and functional status of smoking patients with persistent asthma. Subjects and methods. Examinations were made in 16 healthy smokers (a control group), 22 healthy nonsmoking volunteers (a volunteer group), and 16 patients with endogenous (n=6) and mixed (n=10) persistent asthma (a study group) with varying disease control. The investigators used the following techniques: spirometry; determination of airway resistance and FeCO in the expired air; 30-minute percutaneous monitoring of blood oxygenation and 6-minute walk test; enzyme immunoassay for matrix metalloproteinase levels. Results. The longer duration and higher intensity of smoking increase airway inflammation in the asthmatic patients and the length of blood oxygenation within the very low range. The combined negative influence of tobacco smoking and the underlying disease leads to a clinically significant decrease in pulmonary ventilation ability and basic levels of blood oxygenation, the occurring asthma control reduction being correlating with the longer duration of treatment. The investigators revealed the predictors of lowering the mean level of blood oxygenation (MMP-9, FeCO, and airway resistance), as well as the factors that negatively influence the level of dyspnea and fatigue in asthmatic smokers. Conclusion. The serum levels of FeCO and MMP-9 may serve as markers reflecting the intensity of airway inflammation in smokers with persistent asthma.