200 coal miners without any obstructive ventilatory impairment and presenting small opacities of pneumoconiosis were submitted to respiratory function tests including: spirography, CO transfer test by both steady-state and single-breath methods, and arterial blood gas analysis at rest. 38% do not show any significant abnormalities in the different tests. How ever, 9% presented a discrete hypoxemia at rest imputable either to distribution inequalities in 43.5%, to diffusion impairment in 14%, or less frequently to shunt effects.The frequency of diffusion impairment increases with the extent of radiological abnormalities. No radio-functional correlations were observed for distribution inequalities and hypoxemia.