We explored the usefulness of the postnatal ferret as a model for early developmental events in the large airways, using light and scanning electron microscopy. In the first 28 postnatal days, ferret tracheal surface epithelium and glands undergo dramatic growth and development. Tracheal surface area increases 8-fold. At birth, ciliated cells are sparse (9.4 ± 1.2% of total epithelial cells). A significant increase in ciliated cells is observed at weekly intervals and by day 28 the ciliated cell is the predominant cell type (54.2 ± 2.8% of total epithelial cells). Secretory cells decrease from 66.4 ± 1.0% at birth to 22.2 ±2.8% of total epithelial cells. Histo chemical staining of the granules of the epithelial secretory cells changes from predominantly non-acidic (staining with PAS but not Alcian blue) to predominantly acidic (staining also with Alcian blue). During the same time interval, tracheal glands develop from intra-epithelial cellular aggregates devoid of secretory granules at birth into complex, submucosal tubuloacinar structures composed predominantly of cells containing nonacidic secretory granules at 28 days. Therefore, infant ferrets offer an opportunity to examine the structural and functional components of the mucociliary clearance mechanism at developmental stages which occur prenatally in many laboratory animals and in humans.