Abstract Salt tolerance in Saccharomyces cerevisiae is a complex trait, involving regulation of membrane polarization, Na + efflux and sequestration of Na + in the vacuole. Since transmembrane transport energized by H +-adenosine triphosphatases (ATPases) is common to all of these tolerance mechanisms, the objective of this study was to characterize the responses of the plasma membrane H +-ATPase, vacuolar H +-ATPase and mitochondrial F 1F 0-ATPase to NaCl stress. We hypothesized that since the vacuolar ATPase is responsible for generating the proton motive force required for import of cations (such as Na +) into the vacuole, strains lacking this activity should be hypersensitive to NaCl. We found that strains lacking vacuolar ATPase activity were in fact hypersensitive to NaCl, while strains lacking ATP synthase were not. This effect was specific to the ionic component of NaCl stress, since the mutant strains were indistinguishable from wild-type and complemented strains in the presence of sorbitol.