Claudins and occludin are integral membrane proteins at tight junctions (TJs). We examined subcellular localization of claudin-5 and occludin in dermal vascular endothelia. Immunofluorescence staining showed that claudin-5 was expressed at the cell-cell border of dermal vascular endothelia in mouse skin. However, in some dermal vessels, claudin-5 expression was markedly decreased or absent in amount by double-immunofluorescence stainings with PECAM-1 and PAL-E. In contrast, occludin was not detected in dermal vessels. Freeze-fracture and immunoreplica electron microscopy on primary-cultured human dermal endothelial cells showed that claudin-5 was localized at tight junctions. These findings confirmed that TJs in dermal vascular endothelial cells are composed of claudin-5.