Tracheobronchial aspirates were obtained from 27 normal horses and from 57 horses with respiratory disease. Aspirates from normal horses contained mainly ciliated columnar epithelial cells, mononuclear cells, a few neutrophils and mucus. Aspirates from horses with acute suppurative bronchopneumonias or chronic bronchiolitis had predominantly neutrophils and usually large amounts of mucus; in severe suppurative inflammatory diseases, many of the cells were degenerated, and there were coils of fibrinous material resembling Curschmann's spirals. Eosinophils were rarely found, even from horses with histories suggestive of allergic respiratory disease. Aspirates from horses with epistaxis frequently had macrophages with intracytoplasmic green globules (hemosiderin). Tracheobronchial aspirates occasionally revealed subclinical lung disease. Four horses with no clinical signs of lung disease and lungs that were unremarkable on percussion and normal on auscultation had adpirates suggestive of inflammation; histologic examination confirmed bronchiolitis.