Mechanical injury to ciliated and goblet cells of the rat tracheal epithelium results in sloughing of these cells. The basal cells of the pseudostratified epithelium remain. These cells, studied by scanning electron microscopy, transmission electron microscopy, and en face light microscopy after silver staining, are rounded and separated from one another for the first 2 hours after injury. They become flat and are apposed to each other by 4 hours after injury, but inter-cellular junctions are not uniformly present until 6 hours after injury. By that time, early evidence of stratification of cells is observed, and lanthanum hydroxide, as a colloidal tracer placed in the tracheal lumen, is excluded from the spaces between cells. The changes are indicative of rapid restoration of barrier function after mild injury to the respiratory tract lining as a first step in the reparatve process.