Objective: The epithelial sodium channel (ENaC) probably is a heterotrimer with three well characterized subunits (abg). In humans an additional d-subunit exists with unknown function. ENaC is mainly expressed in sodium transporting epithelia but has also been found in skin, endothelial cells, vascular smooth muscle, and neurons. ENaC expression has also been reported in ocular tissues but its localization and physiological role in the eye are still unclear. Here we analyzed the differential expression of the four ENaC subunits in the human eye. Methods: Quantitative RT PCR was used to investigate the expression of a-, b-, g-, and dENaC transcripts in ocular tissues. For immunocytochemistry we were able to generate subunit specific antibodies against human b- and gENaC but not against a- and dENaC. The specificity of the antibodies was confirmed by immunohistochemistry in human kidney tissue and by Western Blot analysis using the HEK293 overexpression system. Results: Immunohistochemistry revealed that b- and gENaC subunits are present in human retina, choroid, iris, trabecular meshwork, ciliary epithelium, and ciliary muscle. In the cornea and conjunctiva, the keratinocytes contain b- and g- subunits, whereas the corneal epithelium lacks the b-subunit (g is present). In the limbus the b-subunit is localized in basal and the g-subunit in suprabasal cells. In the conjunctiva the b-subunit is exclusively seen in basal cells. Overall, the PCR results were in good agreement with the immunohistochemistry data. In addition, PCR revealed expression of aENaC in cornea, ciliary body, iris, lens, trabecular meshwork, retina, and choroid and of dENaC in ciliary body, iris, lens, retina, and choroid. Conclusion: All four ENaC subunits are expressed in the human eye with a distinct localization of subunits possibly reflecting different functional states of the channel. Further studies will be needed to elucidate the (patho-)physiological role of ENaC in the eye.