The appearance of neutrophils in the alveoli of the lung is a common result of pulmonary infection, although the route of neutrophil migration across the alveolar wall has not been demonstrated in normal animals. Recently, however, several methods of stimulating the influx of neutrophils into alveoli have been developed. In the present study, the lung wash model was used to attract large numbers of neutrophils into the airways in order to identify the site of influx of alveolar neutrophils. The combined use of scanning and transmission electron microscopy has made it possible to visualize the migration of neutrophils from the capillaries, through the interstitial spaces, and through the epithelium at the junctions between Type I and Type II cells.