Extensive analyses of the bacterial flora living in our mouths have been carried out, primarily by cultivation in laboratory media. Using direct PCR amplification of 16s rDNA sequences present in tooth plaque, Relman and co-workers have now shown that many more bacterial species are present in this environment than was previously thought1xBacterial diversity within the human subgingival crevice. Kroes, I. et al. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 14547–14552Crossref | PubMed | Scopus (354)See all References1. The phylotypes (defined as sequences differing by <1%) they were able to recover by direct PCR amplification were significantly more diverse than the phylotypes recovered by in vitro cultivation. The possible roles of these new non-cultivatable bacterial species in oral ecology are unknown. We are clearly only beginning to understand the complexity of the microbial communities within each one of us.