The ultrastructure of the epithelium of terminal bronchioles in healthy control rabbits was evaluated quantitatively. The simple epithelium of terminal bronchioles was composed of ciliated cells and secretory Clara cells. The ciliated cells were low columnar or cuboidal, their apical surfaces carried only several tens of kinocilia that were not arranged to the continuous ciliary border. The high, columnar Clara cells overtopped and often even overlapped the ciliated ones by their voluminous apical portions. The ultrastructure of both cell types was found conformable to this described in the literature. The Clara cells slightly prevailed in number. They represented 52.7 +- 3.6% of epithelial cells. In 73.5 +- 9.4% of them secretory granules were discovered.