Helicobacter pylori cagA transcription and translation are maximal at pH 6 in stationary phase. The aim of this study was to determine whether H. pylori has an acid-tolerance response and whether that response is related to CagA expression, by investigating whether preexposure to pH 5 or 6 improved survival of cells subsequently exposed to pH 3. Cell number was determined after broth growth, after exposure to pH 5, 6, or 7, and then after a 30-min exposure to pH 3 without urea. H. pylori cells preexposed to pH 6 or 5 survived pH 3 exposure 100-fold better than did cells preexposed to pH 7. Cells of cagA+ strains grown at pH 6 for 48 h, which induced maximal CagA expression, were significantly more susceptible to pH 3 than were wild type cagA- strains or isogenic cagA- knockouts. Thus, H. pylori strains possess a urea-independent acid-tolerance response. Differential acid susceptibility may contribute to preferential colonization of particular H. pylori strains in specific mucus layer niches.