Bacterial infections are a common cause of chronic obstructive pulmonary disease exacerbations. They play a main role in exacerbation of cystic fibrosis, less frequently in COPD and occasionally in asthma. Etiology of exacerbations depends on the severity of these diseases and is known to be facilitated by bacterial colonization of the airways. The clinical presentation of bacterial exacerbations is similar and their course is influenced by prompt and proper antibiotic treatment. The principles of this treatment are discussed in the paper.