The fine structure of the main excretory duct epithelium (MEDE) of female mouse submandibular gland was investigated by scanning and transmission electron microscopy and the results compared with the previously established structure of male mouse MEDE. A comparative analysis of the subepithelial capillaries of both sexes was also performed. In this pseudostratified epithelium, principal cell-types were observed: types-I, -II, -III and basal cells. This differed significantly from male MEDE, where type-II and -III are absent and type-I cells are the most numerous. The latter cell-type had abundant mitochondria, a few lipid-containing granules, lysosomes in the infra-nuclear cytoplasm and well-developed basal infoldings. These cells were also characterized by abundant glycogen granules throughout the cytoplasm, many profiles of strands of smooth endoplasmic reticulum in the apical region, and lysosomes in the infranuclear region. Type-II cells were the second most numerous. Their most characteristic features were the presence of tubular vesicles which appeared to be invaginated from the plasma membrane, RER, SER, free ribosomes, a few peroxisomes with nucleoids, and primary lysosomes in extremely light cytoplasm. They had many mitochondria throughout the cytoplasm, except in the apical region, a few lipid-containing granules and no basal infoldings. Type-III cells were very few and were characterized by well developed basal infoldings, abundant free ribosomes, RER, SER, vesicles containing moderately dense material, and many lipid-containing granules. They also had many mitochondria throughout the cytoplasm, except apically. Basal cells had a large nucleus and the cytoplasm had few organelles.(ABSTRACT TRUNCATED AT 250 WORDS)