The calcium-binding proteins calmodulin and S-100 protein alpha and beta subunits were studied in Rat submandibular salivary gland using monoclonal antibodies and immunoperoxidase staining. Histologically, Rat submandibular gland consists of acinar and ductal components. The latter include intercalated, granular convoluted tubule, striated and excretory ducts. Ultrastructural studies of adult Rat granular convoluted tubule show granular cells, pillar cells and transition cells. Immunostaining for S-100 alpha and calmodulin was observed in granular convoluted tubule pillar cells and transition cells, whereas cells of striated ducts and intercalated ducts stained positive for calmodulin. S-100 beta staining in acinar cells was visible as a fine granular pattern. Although immunohistochemical localization in rat submandibular gland differed for S-100 alpha and beta subunits, expression was similar for S-100 alpha and calmodulin in the granular convoluted tubule segment. No immunodeposition of calmodulin, S-100 alpha or S-100 beta was found in granular cells, which contain growth factors such as EGF and NGF.