The aim of this study was to evaluate diagnostic value of capnography for early detection of lung function disorders in smokers. Methods. We compared results of capnography and spirometry and selected the most informative capnographic parameters in three groups of patients (n = 25 each): in non-smokers with normal spirometry, in smokers with normal spirometry and both in smokers and non-smokers with airway obstruction. Curves were obtained for continuous measurement of CO2 partial tension (PCO2) against time and volume. Results. A significant increase in the slope of capnographic alveolar phase during both tidal and deep expiration and a tendency to alveolar hyperventilation were found in obstructive patients. Similar, but less prominent results were obtained in smokers with normal spirometry. Conclusion. Capnography could be useful for early detection of lung function disorders in smokers before preceding occurrence of spirometric abnormalities (airway obstruction). PCO2 measurement against time was the most valuable parameter.