Two definite types of cells, provisionally designated dark and light, in accordance with the degree of their superficial argyrophilism, are revealed in the terminal bronchiolar epithelium of the albino mouse by supravital silverization. The dark cells are ciliated, and scattered among the light unciliated cells as singles, pairs, triads, or larger groups to form a striking and characteristic surface pattern. The cuticles of the dark cells, far outreached by the neighboring light cells, appearen faceas dense crowds of small uniform golden brown granules. Viewed laterally these show as pairs in vertical alignment, and make two layers with a thin lighter band between. The sides and bases are indicated by deposits of black grains. Near the sharply marked margin of the definitive epithelium the dark cells are shorter, more dispersed, and formed like truncated pyramids with narrow densely impregnated apices on some of which are single delicate points instead of discrete cilia. The light cells have bulging villuslike free ends and make flutings on the contiguous dark cells. Small silverized particles sparsely stipple their air surfaces and rounded plaques crown their summits. A similar dicellular picture is found in the terminal bronchiolar epithelium of the golden hamster.