The histological structure of these glands was examined in male rats in two adult age groups. In the submandibular gland, the proportional volume of acinar tissue at 6 months was reduced by 17 per cent at 24 months, being replaced partly by an increased proportion of ducts and partly by increased fibrosis. No volumetric changes occurred in the granular tubules. In the sublingual gland, no volumetric changes were detected in any component tissues. The findings support the concept that biological ageing in the salivary glands does not occur as a uniform generalized process throughout all the salivary tissues.