In a previous investigation of bifidobacteria isolated from human dental caries (V. Scardovi and F. Crociani, Int. J. Syst. Bacteriol. 24:6-20, 1974), 40 strains were assigned to the new species Bifidobacterium dentium. In this study we examined 70 new strains of bifidobacteria isolated from dental caries. The morphological characteristics, biochemical reactions, fermentation patterns, end products from glucose metabolism, protein electrophoretic patterns, levels of DNA hybridization, and DNA G+C contents of these organisms revealed that they belong to three different taxa. One of these taxa was identified as B. dentium. The other two are described as the following new Bifidobacterium species in this paper: Bifidobacterium inopinatum (type strain, DSM 10107) and Bifidobacterium denticolens (type strain, DSM 10105). The two new species differ from other Bifidobacterium species in their morphological characteristics (especially B. inopinatum, with its very small coccoid cells), in their carbohydrate fermentation patterns (most strains ferment dextran, and B. inopinatum does not ferment galactose), and in their DNA base compositions (especially B. inopinatum).