The significance of physical exercise and attempts of detecting early pulmonary fibrous lesions using resultant parameters were described in cases with pulmonary fibrosis and pneumoconiosis. Although the usefulness of A-aDo2 has been pointed out long before the use of the respiratory index (A-aDo2/Pao2×100) instead of A-aDo2 itself was thought to be more effective. In relation to this, the change of the pulmonary diffusing capacity associated with physical exercise was thought to reflect the pulmonary reserve capacity. As regards the ventilatory function, the usefulness of the ventilatory index, exercise index and VD/VT was suggested by the present study.