Carbonic anhydrase (CA) has been localized to many structures involved in ion transport including the acini and ducts of the major (parotid, sublingual and submandibular) salivary glands of humans and rodents. It also has been localized by enzyme histochemistry and by immunohistochemistry for CA isoenzyme VI (CA VI) to the acini and ducts of rat serous lingual glands of von Ebner. The purpose of this study was to explore the intracellular distribution by cell type of three CA isoenzymes in these glands. Immunohistochemistry was undertaken with antibodies to human CAs I, II and VI in paraffin sections of rat tongues that had been fixed in Helly's fluid. The density of the reaction product was scored as 0 (none) to 5 (strongest). Reactions in the acini with CA I and II antibodies were weak luminally to moderate basally and generally moderate, respectively, moderate in the intercalated ducts, and moderate basally to strong luminally in the excretory ducts. Weak to moderate CA VI reactions occurred in the acini and ducts. The stronger luminal reactions to CAs I and II in the excretory ducts suggest that they contribute to pH regulation in the saliva of von Ebner's glands via HCO3- transport.