The non-ciliated epithelial cells in the air way of mice were examined by electron microscopy. They are flask-like or pyramidal cells dispersed singly or occasionally in pairs. The apical portion of the cells reaches the air way lumen with microvillous projections. Their cytoplasm always contains abundant and variable numbers of small granules (60-170 nm in diameter). Close appositions between non-ciliated cells and nerve fibers are frequently observed at their lateral or basal surfaces. Fine structures of the non-ciliated cells are similar to those previously reported in the cells under different designations such as brush cells, basal-granulated cells, cells of neuroepithelial bodies and endocrine cells. The present study proposes that these names express different features of the same cell group collectively called "non-ciliated cells" in this paper. Furthermore images indicating exocytotic granule release are obtained in this study, indicating an endocrine function of these cells.