Nine Campylobacter-like strains were isolated from human gingival crevices and characterized. These strains were gram-negative, straight rods that were motile by means of multiple unipolar flagella. They were asaccharolytic and preferred an anaerobic atmosphere rather than a microaerophilic atmosphere for growth, and their growth was stimulated by formate and fumarate. These strains were biochemically similar to Campylobacter curvus and Campylobacter rectus, but were clearly distinguishable from these organisms by the number of flagella (two to five flagella at one end of the cell), by being catalase positive, by their whole-cell protein profiles, by their Western blot (immunoblot) patterns, and on the basis of DNA-DNA homology data. They could also be differentiated from the other species of the genus Campylobacter. The nine Campylobacter-like strains were compared with two strains (FDC 286 and VPI 10279) representing a previously described but unnamed Wolinella sp. The nine isolates and strains FDC 286 and VPI 10279 were found to be members of a single species. The 16S rRNA sequences of two strains of the newly identified species were compared with the rRNA sequences of 21 reference Campylobacter, Wolinella, and Helicobacter species in order to generate a phylogenetic tree. We propose the name Campylobacter showae for the newly identified strains; strain SU A4 (= ATCC 51146) is the type strain of this new species.