Alveolar macrophages attack various foreign bodies inspired through the airway and destroy cell debris. Furthermore, a part of the surfactant produced by alveolar epithelium would be phagocytized by alveolar macrophages forming foamy cells in lung tissue. These formy cells could be detected by oil red O staining as xanthoma cells in sputa of patients with airway diseases. Therefore, xanthoma cells in sputa of patients with DPB, chronic bronchitis and bronchial asthma were evaluated to clarify the role in the pathogenesis of these respiratory diseases. All patients with DBP expectorated enormous amounts of xanthoma cells in sputa while 88% of the patients with chronic bronchitis and 41% of those with bronchial asthma had sputa containing xanthoma cells in a smaller number than DBP. Increased xanthoma cells were shown in DPB with longer disease duration, lower vital capacity, lower atrerial blood oxygen pressure, and pseudomonas infection. However, extreme obstruction of small airway diminished xanthoma cells in sputa. Xanthoma cells were shown in bronchial asthma especially in late onset and intractable asthmatics. These findings indicate that xanthoma cells in sputa reflect the existence of organic changes in the small airway which disturb the drainage of surfactant from alveolar area to bronchial trees.