Most striated duct (SD) cells in the adult mouse parotid gland (PAG) have a few small secretory granules. These granules, however, are usually too small and sparse to be detected using light microscopy. Our serial studies have suggested that these PAG SD cells belong to a group of hormone-responsive granular duct cells, similar to the granular convoluted tubule (GCT) cells found in the submandibular gland. These studies also indicate that and some PAG SD cells may be capable of developing a granular cell phenotype under supraphysiological conditions of androgenic and thyroid hormones, leading to more abundant, and more kinds of GCT-specific secretory polypeptides. Here, the cytology of hormone-modulated SD cells, the immunocytochemistry of their secretory products, and their secretory responses to some autonomic agents are reviewed. Finally, the close similarity of the duct systems of the three major salivary glands in mice is critically emphasized.