AbstractHere, we investigated the expression of the claudin family of tight junction transmembrane proteins in the developing mouse submandibular gland. Data obtained by reverse transcriptase‐polymerase chain reaction, Western blot, and immunofluorescence microscopy showed the expression and localization of claudin‐3 to ‐8, ‐10, and ‐11 at epithelial tight junctions. Examination of the glands taken from embryonic day (E) 14, E16, and newborn mice revealed differential expression patterns of these claudins in the developing epithelium. Claudin‐3, ‐5, and ‐7 were expressed in all of the luminal epithelial cells of the ducts at all of the developmental stages examined and in those of terminal tubules at E16 and later. Claudin‐4 was expressed mainly in the ducts at all the developmental stages. The expression of claudin‐6 and ‐8 was also restricted to the ducts at E14 and E16; but after birth, the former was undetectable, whereas the latter was expressed in both the ducts and terminal tubules. Claudin‐10 and ‐11 were detectable mainly in the terminal tubules at E16 and later. In addition to being found in the epithelium, claudin‐5 was also expressed in certain mesenchymal cells, probably endothelial cells. These results will provide a valuable resource for further investigation of tubulogenesis and physiological regulation of claudin‐based tight junctions. Developmental Dynamics 231:425–431, 2004. © 2004 Wiley‐Liss, Inc.