A group of 908 subjects has been studied, of which two-thirds were males, classified in 5 categories: unexposed, with light exposure, and severely exposed to inhalation of volatile substances, or various types of dust. A B.M.R.C. file was filled for each of the subjects. This file concerns respiratory symptoms. A forced expirogram was also performed, and FEV 25-75%, FEV 75-85%, and TEM were determined. The two expiratory flows (median and final) are frequently disturbed in subjects without respiratory symptoms, more frequently in smokers with a normal FEV 1. In those exposed to respiratory risk the proportion of alterations increases, but association of smoking with inhalation of noxious chemical substances will determine a modification of FEW 1 and anomalies of the peripheral bronchi occur more frequently in smokers. Between the criteria suggesting the presence of small airways disease, the ratio FEV 25-75% under 60%, with a FEV 1/FVC ratio within normal limits, this being the most sensitive of the criteria, also appears as the most reliable.