Despite the constant presence of members of Bifidobacteriaceae in the human oral cavity, few studies of their occurrence in this habitat have been made. The presence and the distribution in human plaque and dental caries of Bifidobacterium dentium, Scardovia inopinata and Parascardovia denticolens, all belonging to the family Bifidobacteriaceae, were studied. The identification to species level was based on morphological and growth type features, fermentation tests, polyacrylamide gel electrophoresis of the soluble proteins and DNA-DNA homology. The three species, isolated on propionic acid trypticase phytone yeast extract medium, were present in 13 out of 19 and in 11 out of 15 subjects examined for dental caries and plaque, respectively. S. inopinata was the species most frequently isolated in dental caries, whereas B. dentium was more numerous in dental plaque. The prevalence of P. denticolens was similar in the two habitats. In conclusion, the prevalence of bifidobacteria species (B. dentium, P. denticolens, S. inopinata) in relation to non-bifidobacteria isolates was significantly different in caries versus plaque samples (p < 0.0001; χ2 test).