Recent evidence has indicated that natural genetic transformation occurs in Vibrio cholerae, and that it requires both induction by chitin oligosaccharides, like chitohexaose, and expression of a putative regulatory gene designated tfoX. Using sequence and phylogenetic analyses we have found two tfoX paralogues in all sequenced genomes of the genus Vibrio. Like V. cholerae, when grown in chitohexaose, cells of V. fischeri are able to take up and incorporate exogenous DNA. Chitohexaose-independent transformation by V. fischeri was observed when tfoX was present in multicopy. The second tfoX paralogue, designated tfoY, is also required for efficient transformation in V. fischeri, but is not functionally identical to tfoX. Natural transformation of V. fischeri facilitates rapid transfer of mutations across strains, and provides a highly useful tool for experimental genetic manipulation in this species. The presence of chitin-induced competence in several vibrios highlights the potential for a conserved mechanism of genetic exchange across this family of environmentally important marine bacteria.