The plasma membrane Na+-H+ exchanger is a ubiquitous transport system that participates in diverse cell functions involving the cellular uptake of Na+ or extrusion of H+. It has a tightly coupled 1:1 stoichiometry, has affinity for Li+ and NH+4 in addition to Na+ and H+, and can function in multiple amiloride-sensitive exchange modes involving these cations. These general transport properties may be explained by kinetic models involving either cation-hydroxyl cotransport or actual cation-proton exchange. The most important kinetic property of the Na+-H+ exchanger is its greater than first-order dependence on [H+]i. This property enables the Na+-H+ exchanger to play an important role in the regulation of intracellular pH.