The phylogenetic positions of six Vibrio costicola strains were determined by direct sequencing and analysis of their PCR-amplified 16S ribosomal DNAs. A comparative analysis of the sequence data revealed that the moderate halophile V. costicola forms a monophyletic branch that is distinct from other Vibrio species and from moderately halophilic species of other genera. These results complement phenotypic and genotypic data determined previously. The molecular evidence, together with several phenotypic differences, distinguishes V. costicola from species of the genus Vibrio and other species belonging to the gamma subclass of the Proteobacteria and indicates that V. costicola should be placed in a new and separate genus. The name Salinivibrio costicola gen. nov., comb. nov. is proposed for this bacterium. The guanine-plus-cytosine content of the DNA is 49.4 to 50.5 mol%. The type strain of S. costicola is strain NCIMB 701 (= ATCC 33508).