Twenty-eight strains of microaerophilic, motile, slightly curved gram-negative rods isolated from the gingival crevice of patients with gingivitis were studied. They seemed similar to Vibrio sputorum, though eleven strains differed in minor characters from Bergey's description under the new name Campylobacter sputorum, subspecies sputorum. The oral strains studied appeared to be closely related to several species of the genus Campylobacter and to Vibrio succinogenes. The oral strains were able to utilize gaseous hydrogen and to grow in a mineral medium with either nitrate of fumarate as hydrogen acceptor. Formate could replace hydrogen as hydrogen donor. In contrast the Campylobacter strains were not dependent on hydrogen or formate as energy source and grew poorly in mineral medium. In these nutritional and metabolic aspects the oral strains are more related to Vibrio succinogenes than to Campylobacter species. Serologically the oral strains differed from all the Campylobacter species. The GC ratio in the DNA of the oral strains varied between 48 and 50%, conform to the values described for Vibrio succinogenes. Vibrio sputorum seems a nomen conservandum and vibrio-like organisms from human infections should be tested for hydrogen-dependence before they are classified as Campylobacter species.