The submandibular gland of the mouse was studied by high-resolution scanning electron microscopy, using the osmium-dimethylsulfoxide-osmium method. The three-dimensional structures of the intracellular membranous organelles of acinar cells were clearly revealed. The luminal surface of cisterns of the granular endoplasmic reticulum and Golgi apparatus exhibited particles of 8-15 nm in diameter. The secretory canaliculi presented short microvilli which were irregularly arranged. The striated duct cells were characterized by rich mitochondria arranged vertically in the basal portion. The lamellar mitochondrial cristae were noted in three-dimensional images. The luminal surface extended short microvilli, while that of the excretory duct cell presented complicated microplicae. The capillary endotheliocytes showed a few short microvilli, and their fenestrated areas were bordered by cytoplasmic crests. Fenestrae were 50-80 nm in diameter and showed a plug in their center. The basement membranes of the acini and capillaries showed a spongy structure with various strands and meshes. Collagenous fibrils crisscrossed on their surface.