The development of the tracheal epithelium was studied in hamsters, beginning on fetal day 10 and ending on fetal day 16, shortly after birth. The epithelial morphology was characterized and as soon as the cells could be recognized by type (day 14) their proportions were quantified along dorsal and ventral surfaces from larynx to carina. At all times, columnar cells of the dorsal surface were taller than those of the ventral surface. On days 10 and 11 the simple epithelium was composed of poorly differentiated columnar cells, but on day 12 organoid clusters, consistent with the morphology of neuroepithelial bodies, were observed; four clusters were seen along the dorsal epithelium in one section. The epithelium was pseudostratified on day 13, composed of short and columnar cells. Most columnar cells were poorly differentiated but a few preciliated and ciliated cells were recognizable dorsally, especially at the tracheal poles. Hemidesmosomes were seen at the base of some short cells on day 14, and rough endoplasmic reticulum was moderately developed in some columnar cells, suggesting that these cells were prebasal and presecretory cells, respectively. Preciliated and ciliated cells, which were most prevalent caudally, accounted for about 14% of all dorsal epithelial cells on day 14, but they were rare in the ventral surface, about 0.1%. The epithelial cells were sufficiently specialized by days 15 and 16 to allow quantification by type. Proportions of basal, presecretory, and preciliated-ciliated cells were similar on both days but the cellular makeup of dorsal and ventral surfaces was significantly different. There were more basal cells ventrally (36-40%) than dorsally (22-23%), and more preciliated-ciliated cells dorsally (18-21%) than ventrally (about 1%). On days 15 and 16 differences also existed along both surfaces between cranial and caudal parts of the trachea. Basal cells were more prevalent cranially and preciliated-ciliated cells were more prevalent caudally.