Age changes of the submandibular glands (SMG) of male rats were studied morph metrically and ultra-structurally from youth to old age. The most conspicuous feature of the aged SMG was regressive changes of the granular ducts. The extent and height of the granular ducts decreased as well as the content of mature secretory granules. These changes may play an important role for an individual rat, because the granular duct synthesizes many biological factors. Cytoplasmic crystalloids, salivary deposits and oncocytic transformation were also found in the SMG of rats more than 22-months-old. It was noticeable that the intercalated duct cells were especially affected by both crystalloid formation and oncocytic transformation.