The aim of this study was to specify the effect of therapeutic pulmonary lavage on the function of alveolar macrophages in a patient suffering from alveolar proteinosis; we have studied phagocytosis and chemotaxis in cells before and at different times after the lavage. Our results indicate a restoration of the functional properties of the alveolar macrophages in parallel with an improvement in pulmonary function and blood gases under the effects of treatment. These data are in favour with an inhibitory effect of the lipoprotein material on the function of alveolar macrophages and suggest that the deposit of this material is a determining factor in the alteration in the defense mechanisms of the lung.