AB - On five affected but diffuse fibrosing alveolitis (.), four with 'desquamative' pattern and one with 'mural' pattern, we carried-out a clinical, radiological and pathophysiological evaluation before and after treatment. A significant improvement, during was observed during treatment, in four patients with 'desquamative' pattern, from dyspnea, radiological and pathophysiological data (static pulmonary volumes, diffusing lung capacity, Raw MEF 50, MEF 25, static and dynamic compliance). In the one patient with 'mural' pattern we observed a progressive worsening of all parameters. After therapy the complete disppearance of dyspnea and the partial improvement of radiological findings were only partially related to the recovery of volumes and elastic properties. We concluded that in diffuse fibrosing alveolitis the lack of improvement, after treatment, of diffusive lung properties may be related to small airways disease which leads to impairment of ventilation/perfusion ratio. Furthermore, the disappearance of dyspnea might be related to improvement of thoraco-pulmonary mechanics.