Transport of particles from alveolus to bronchiolar exit routes is a vital phase of defense mechanisms in the lung. Alveolar bronchiolar transport may occur along the surface of the alveolar and bronchiolar structures and through interstitial spaces and lymphatic channels. Cell and particle movement is directed (1) onto the bronchial lumen; (2) into subpleural and paraseptal positions; (3) to perivascular positions; and (4) movement to a peribronchial location. The energy for this cell and particle transport is more likely related to fluid transport along interstitial pathways than active ameboid motion. Transport pathways appear to be oriented radially around the terminal bronchiolar system, rather than longitudinally along air pathways. The several anatomic pathways of productive movement from the alveolus to the bronchiole or to lymphatics may account for the apparent clearance compartments found in radiotracer studies and experimental histologic studies. The location of pulmonary lymphoid nodules along the transport pathways provide a mechanism for local intrapulmonary antigen processing and antibody production. The availability of transport pathways directly from alveolus to bronchial surface provides a mechanism for rapid exit of particles and cells from alveolar tissue.