Correct lung function is indispensible to perform work underwater. Thus, spirometric tests of lung function remain an important element in the process of selecting candidates for professional diving. Studies conducted in the population of divers identified the phenomenon called 'large lungs', which is often associated with spirometric indices characteristic of obstructive impairment of lung function. This study investigated selected parameters of lung function in the population of divers and candidates for professional divers. Fifty two male subjects were examined as part of the selection process. Basic spirometric tests: forced expiratory volume in 1 s (FEV1; dm(3)), forced vital capacity (FVC; dm(3)), forced expiratory flow in the range 25-75 % of FVC (FEF25-75; dm(3) s(-1)), and FEV1/FVC (%) were compared with compared with the predicted reference values estimated by the European Coal and Steel Community. The results demonstrate differences in FVC and FEF25-75 in divers, which may correspond to functional hyperinflation. The effects of 'large lungs' observed in divers, if persisting for an extended period of time, may lead to lung ventilation impairment of the obstructive type.