Bacteriological examination of sputum is the simplest and widely accessible diagnostic method of respiratory infections. However its value in nonspecific respiratory infections, especially in exacerbations of COPD, is questionable because they can be caused by factors other than bacterial or by viral infections. The evaluation of bacteriological examination of sputum in patients with exacerbations of COPD and the evaluation of interaction between clinical course, some laboratory markers and bacteriology of sputum was the aim of the study. 109 patients hospitalized with exacerbations of COPD were examined. Semi-quantitative bacteriological examination of sputum, total blood count, erythrocytes sedimentation rate, gasometry and spirometry were performed in each patient. The identification of pathogens was conducted by microtests API from Bio-Merieux. In 39 patients (36%) pathogenic bacteria were cultured from sputum. The most prevalent organisms were: A. baumanii-21% and S. aureus-17%. Positive culture was seen most often in patients with severe and very severe COPD. Bacterial infection as a cause of COPD exacerbation should be suspected especially in patients with severe-staged disease of long duration, when bacterial cells and predominant neutrophil-count are present in sputum. In patients with severe COPD, often treated in hospital and with antibiotics, Gram-negative flora should be considered as an etiologic agent.