An epidemiological study of 1,178 iron-mine workers in the Lorraine basin was conducted in order to assess the long-term effects on the respiratory system of low concentrations of noxious gases produced by the machinery and explosives in use. The subjects were selected at random from 5,300 workers who were aged between 35 and 55, had been in the mines for at least five years and who were free from radiological abnormalities such as siderosis, tuberculosis, fractured ribs, etc. For each subject a standard questionnaire (E.C.S.C. bronchitis/emphysema questionnaire) was completed and a clinical examination was performed along with the following tests-vital capacity; forced expiratory volume in 1 second; residual volume; acetylcholine test; steady state CO test for calculation of total and partial transfer functions. A venous blood sample for the determination of blood CO was taken as the subject left his place of work.