Scientific studies of the material obtained during bronchial biopsy, bronchoalveolar lavage and sputum induction altered the view on the pathogenesis of asthma and COPD. In the result, both bronchial diseases are considered inflammatory. Eosinophils play the main role in the pathogenesis of asthma, whereas in COPD the most significant are neutrophils. Bronchial biopsy and bronchoalveolar lavage have been applied mainly in scientific studies, while sputum induction as a non-invasive method can be useful in everyday practice too. Increased level of eosinophils in sputum allows to forecast the efficiency of glucocorticosteroids in the therapy of asthma and COPD.