Studying the cellular products obtained by broncho-alveolar lavage in 81 patients, 77 coal-miners and 4 other subjects exposed to silicotic risks of various origin, the authors could demonstrate the interest of this new method of exploring the peripheral lung tissues. In 57 cases of usual pneumoconiosis and controls matched for the smoking habits, the repartition of the different cellular types was quite similar. On the contrary, the authors observed an increase of the lymphocytes in three cases of accelerated elution of the pneumoconiosis. Moreover various modifications were noticed in cases with morbid associations as conectivitis, sarcoïdosis, allergic alveolitis, and primitive diffuse interstitial fibrosis as well. At the moment they were collected, the alveolar macrophages of the subjects to dust showed the same properties of vitality and adherence capacity as the controls. After 24 hours of survival their vitality and bacterial activity on staphylococcus aureus was clearly diminished.