Asthma and COPD are characterized by changeable narrowing of airways called bronchi obstruction. This obstruction is evoked by mucosal inflammation and remodelling which is also the result of recruitment of inflammatory cells and acting different mediators and cytokines. Varies structures and processes named epithelial- mesenchymal trophic unit are active in inflammatory process. Diagnosing of asthma is based on history, allergological examination and evaluation of spirometry parameters. The FVC, FEV1, FEV1 FVC ratio are the basic parameters used to properly interpret lung function. The severity of pulmonary function abnormalities is based on FEV1% predicted. The characteristic feature of asthma is changeability of clinical symptoms and spirometry parameters. The most important parameter for identifying an obstructive impairment in patient is FEV1 FVC ratio. The typical spirometry parameters shown are: normal FVC, decreased FEV1 and FEV1 FVC ratio. Sometimes FVC and FEV1 are concomitantly decreased and the FEV1 FVC ratio is normal or almost normal. The part of lung function is bronchial reversibility test. An increase in FEV1 and/or FVC 12% of control and 200 ml constitutes a positive bronchodilator response. The aim of this test is to determine whether the patient’s lung function can be improved after 400 μg inhalation of salbutamol or after treatment for 2-8 weeks with inhaled glycocorticosteroid. Spirometry parameter allow us to evaluate the severity of illness and possible therapeutic intervention. For asthma diagnosing and evaluation of treatment nonspecific airways responsiveness should also be measured. Bronchial hyperresponsiveness is very sensitive but not specific tool for the diagnostic purpose. Negative result of inhaled provocative test with methacholine allows to exclude asthma, positive result confirms the diagnosis of asthma in doubtful cases with non-typical symptoms when improvement of spirometry after bronchodilator administration is not observed. Monitoring of bronchial hyperresponsiveness in time of treatment of asthma allows to achieve better control of asthma also.