Objectives: The amiloride-sensitive epithelial Na⁺-channel (ENaC) regulates Na⁺ homeostasis across several epithelia cells. In human nasal epithelium (HNE) the three classically expressed subunits (a, b,g) and an additional subunit (d) are constantly expressed. Up to now little is known about the physiological role and the functional properties of the d-ENaC subunit. Here, we compared the presence and functional expression of the d- and a-ENaC subunit in HNE. Methods: We compared the cell surface expression of the d-subunit with the classically expressed a-subunit by using immunofluorescence experiments. Thus, we used specific anti-ENaC antibodies, which bind to the extracellular loop and QD-labelled anti-rabbit F(ab´)2 conjugates as secondary antibodies. Moreover, we were interested in the portion of the d-ENaC mediated Na⁺ current, which could be distinguished from the total amiloride-sensitive current in Ussing chamber experiments by the specific blocker Evans Blue. To verify the specificity of Evans Blue we downregulated d-ENaC expression with siRNA. In another set of experiments we demonstrated that the d-ENaC activator icilin increases Na⁺ transport in HNE. Results: The immunofluorescence analyses showed that the quantity of a- and d-ENaC is almost comparable (a-ENaC: 0.164 ENaC molecules/mm²; d-ENaC: 0.146 ENaC molecules/mm²), suggesting that in HNE both subunits are expressed in a similar manner. Interestingly, Ussing chamber experiments demonstrated that in HNE a large portion of the Na⁺ transport is mediated by the d-ENaC subunit. Conclusion: Immunofluorescence and functional measurements support the presumption that the d-ENaC subunit plays a prominent role in the whole Na⁺ transport in this particular tissue. Our data confirm and extend the existing knowledge with regard to ENaC distribution and function.