The vacuolar proton-pumping ATPase (V-ATPase) is responsible for the acidification of intracellular organelles and for the pH regulation of extracellular compartments. Because of the potential role of the latter process in olfaction, we examined the expression of the V-ATPase in mouse olfactory epithelial cells. We report that V-ATPase is present in this epithelium, where we detected subunits ATP6V1A (the 70-kDa "A" subunit) and ATP6V1E1 (the ubiquitous 31-kDa "E" subunit isoform) in epithelial cells, nerve fiber cells, and Bowman's glands by immunocytochemistry. We also located both isoforms of the 56-kDa B subunit, ATP6V1B1 ("B1", typically expressed in epithelia specialized in regulated transepithelial proton transport) and ATP6V1B2 ("B2") in the olfactory epithelium. B1 localizes to the microvilli of the apical plasma membrane of sustentacular cells and to the lateral membrane in a subset of olfactory sensory cells, which also express carbonic anhydrase type IV, while B2 expression is stronger in the subapical domain of sustentacular cells. V-ATPase expression in mouse olfactory epithelia was further confirmed by immunoblotting. These findings suggest that the V-ATPase may be involved in proton secretion in the olfactory epithelium and, as such, may be important for the pH homeostasis of the neuroepithelial mucous layer and/or for signal transduction in CO2 detection.