Two proton-transporting ATPases participate in active proton transport in the nephron: the electrogenic vacuolar H+-ATPase and the electroneutral H+-K+-ATPase. The vacuolar H+-ATPase participates in proximal and distal hydrogen ion secretion related to acid-base homeostasis. The H+-K+-ATPase is located exclusively in the distal nephron, and its primary role may be in active potassium reabsorption. The properties, distribution, and regulation of these two enzymes are discussed.