This review discusses the molecular identites and functional properties of sodium-independentCI--HCO3- exchangers in the kidney. The main sites of renalCh-HCO3- exchange are in the intercalated cells of the collecting duct. The function ofCI--HCO3- exchange is to provide a pathway for base efflux to balance the ATP-driven H+ efflux in cells that carry out transcellular net transport of H+. In the a-intercalated cell, which secretes H+ into the lumen, there is now excellent evidence that the basolateralCI--HCO3- exchanger is an N-terminal truncated form of the erythrocyte anion exchanger 1 (band 3) protein. In the p-intercalated cell, which secretesHCO3-, it is well established that there is aCh-HCO3- exchanger in the apical membrane. Functional, immunocytochemical, and biochemical evidence indicate that the apicalCI--HCO3- exchanger is not a product of the anion exchanger 1 gene. The identity of this protein remains uncertain.