Non-smoking, male, professional firemen divers (n = 15) underwent two pulmonary function tests (PFT) separated by 6 years. Measured data were compared to European Coal Steel Community recommended reference values to permit cross-sectional and then longitudinal study. Higher vital capacity (VC; P < 0.01) and forced expiratory volume in 1 s (FEV1; P < 0.05), and lower maximal mid-expiratory flow (MMEF) coefficient with VC (MMEF/VC; P < 0.05) were observed in both PFT. Diver's pulmonary diffusing capacity (DL(CO)) and the coefficient with alveolar volume (DL(CO)/V(A)) showed significantly (P < 0.001) different evolution profiles than those expected from predicted values. In divers, DL(CO) and DL(CO)/V(A) decreased from 104.0% to 91.4% and from 106.4% to 91.5% of predicted values respectively. Changes in DL(CO) and DL(CO)/V(A) correlated positively with the initial measurement of DL(CO) (r = 0.67, P < 0.01) and DL(CO)/V(A) (r = 0.74, P < 0.01) respectively, whereas no correlation between changes in pulmonary gas transfer function and age or diving history parameters was found. Thus, it is suggested from our observations that hyperbaric atmosphere exposure increases the effects of aging on pulmonary diffusing capacity and that pulmonary gas transfer function should be regularly tested in professional and recreational divers.