Tight junctions are the most apically positioned intercellular junction and play many roles such as securing adjacent cells, forming barriers from extracellular materials, and facilitating paracellular transport. Occludin and junction adhesion molecule A (JAM-A) are classified as transmembrane proteins that are directly involved in paracellular transport. Zona occludens-1 (ZO-1) is a protein that contains a PDZ domain which forms a binding site for other tight junction proteins. In this study, we assessed the differential expression of these tight junction components in various mouse organs including the intestine (duodenum, ileum, and colon), kidney, liver, lung, brain, and skeletal muscle. Realtime PCR and Western blot assays were performed to measure the gene and protein expression of occludin, JAM-A, and ZO-1. Similar levels of occludin gene expression were detected in all tissues except for skeletal muscle in which occludin expression was not found. The JAM-A and ZO-1 genes were highly expressed in all the tested tissues. Localization of occludin, JAM-A, and ZO-1 was determined by immunohistochemistry. These proteins were detected in the intercellular apical junctions in each tissue except for occludin (which was not observed in skeletal muscle). These immunostaining data were consistent with the gene expression profiles we obtained. Our results suggest that occludin, JAM-A, and ZO-1 genes are normally expressed in the intestine, kidney, liver, lung, and brain indicating that these factors may be essential for maintaining appropriate physiological concentration of ions, solutes and water.