Renal epithelial Na⁺transport plays an important role in homeostasis of our body fluid content and blood pressure. Further, the Na⁺transport in alveolar epithelial cells essentially controls the amount of alveolar fluid that should be kept at an appropriate level for normal gas exchange. The epithelial Na⁺transport is generally mediated through two steps: (1) the entry step of Na⁺via epithelial Na⁺channel (ENaC) at the apical membrane and (2) the extrusion step of Na⁺via the Na⁺, K⁺-ATPase at the basolateral membrane. In general, the Na⁺entry via ENaC is the rate-limiting step. Therefore, the regulation of ENaC plays an essential role in control of blood pressure and normal gas exchange. In this paper, we discuss two major factors in ENaC regulation: (1) activity of individual ENaC and (2) number of ENaC located at the apical membrane.