Prevotella tannerae sp. nov. and Prevotella enoeca sp. nov. from the human gingival crevice are described. These organisms are obligately anaerobic, non-spore-forming, nonmotile, gram-negative, rod-shaped bacteria that ferment carbohydrates and produce succinic and acetic acids. Bile inhibits growth. Some strains (38%) of P. tannerae produce colonies with a tan to black pigment when they are grown on rabbit blood agar. The type strains are P. tannerae ATCC 51259 and P. enoeca ATCC 51261. In addition, the description of Prevotella zoogleoformans is emended to exclude strains now recognized as members of Prevotella heparinolytica.