The ability to move toward favorable environmental conditions, called chemotaxis, is common among motile bacteria. In particular, aerotaxis has been extensively studied in Escherichia coli and was shown to be dependent on the aer and tsr genes. Three putative aer gene homologs were identified in the Vibrio cholerae genome, designated aer-1 (VC0512), aer-2 (VCA0658), and aer-3 (VCA0988). Deletion analyses indicated that only one of them, aer-2, actively mediates an aerotaxis response, as assayed in succinate soft agar plates as well as a capillary assay. Complementation studies confirmed that Aer-2 is involved in aerotaxis in V. cholerae. In addition, overexpression of aer-2 resulted in a marked increase of the aerotactic response in soft agar plates. No observable phenotypes in V. cholerae mutants deleted in the aer-1 or aer-3 genes were detected under standard aerotaxis testing conditions. Furthermore, the V. cholerae aer-1 and aer-3 genes, even when expressed from a strong independent promoter, did not produce any observable phenotypes. As found in other bacterial species, the results presented in this study indicate the presence of a secondary aerotaxis transducer in V. cholerae.