Cycling of protons and Na+ across bacterial membranes is connected with such vital bacterial functions as are ATP synthesis, pH and Na⁺ homeostasis, motility, and solute transport. The Na⁺/H⁺ antiporter is the universal device that couples these H⁺ and Na⁺ movements across bacterial membranes. The review is concerned with the new aspects of molecular biology and physiology, regulation of activity as well as expression of Na⁺/H⁺ antiporters in E. coli, alkalophilis, halophilis, anaerobic bacteria, and archabacteria. The possible role of Na⁺/H⁺ antiporter in bioenergetic processes in these microorganisms is also discussed.