Chronic obstructive lung disease (COLD) is an important cause of mortality and disability. In a cross-over study, followed by a longitudinal one, of a homogeneous group of blue collar steel workers, we have found that the slope of the N2 alveolar plateau was the most frequently impaired test, in the absence of any respiratory symptom. However, its predictive power was low enough to preclude its use for early detection of COLD. We have now a better understanding of the issues of early detection of COLD, the risk factors involved as well as of the therapeutic intervention to improve its prognosis.