Polyphasic analysis of five new Vibrio isolates originating from the haernolymph of diseased cultured oysters is described. The new isolates were closely related to Vibrio splendidus, having 98 % 16S rRNA gene sequence similarity. gyrB phylogenetic analysis, fluorescent amplified-fragment length polymorphism (FAFLP) fingerprinting and DNA-DNA hybridization experiments clearly showed that the new isolates form a tight genomic group that is different from the currently known Vibrio species. It is proposed to accommodate these isolates in a novel species, Vibrio crassostreae sp. nov. (type strain LGP 7(T) =LMG 22240(T)=Clp 108327(T)). Phenotypic and chemotaxonomic features that differentiate V. crassostreae from other known Vibrio species include arginine dihydrolase, utilization and fermentation of various carbon sources, beta-galactosidase activity, NO2 production and the presence of the fatty acids 14: 0 iso and 16: 0 iso.