Anion exchange plays an important role in renal ion transport and acidification. To further understand the molecular nature of renal epithelial anion exchange, we used a monoclonal antibody to the membrane domain (52 kDa) of human erythrocyte band 3 protein to immunocytochemically search for this polypeptide in the rabbit kidney. In cryostat sections, a subpopulation of cells in the cortical and outer medullary collecting tubules showed immunoreactivity; labeling was restricted to the basolateral membrane. Proximal tubules and thick and thin limbs of Henle showed no immunoreactivity. Approximately 11% of cells in the cortical, but 43% of cells in the medullary, collecting tubule were positive for band 3. To determine the type of cells that were band 3 positive, mitochondria-rich (intercalated) cells were identified by their positive histochemical staining for succinic dehydrogenase activity and by their ability to bind peanut lectin at the apical membrane. In the cortical collecting tubule, the majority of mitochondria-rich cells bound peanut lectin but were band 3 negative; the remainder were band 3 positive but lectin negative. This distribution was reversed in the inner stripe of the outer medulla: all mitochondria-rich cells were band 3 positive and lectin negative. Thus mitochondria-rich cells are of at least two types, each of which has a distinct axial distribution pattern. Given available information about in vitro HCO3 transport properties of rabbit collecting tubules, it is likely that the lectin-positive, band 3-negative mitochondria-rich cells secrete HCO3, whereas the lectin-negative, band 3-positive cells reabsorb HCO3 (secrete H).