SUMMARY: Novel chlamydiae are newly recognized members of the phylum Chlamydiales that are only distantly related to the classic Chlamydiaceae, i.e., Chlamydia and Chlamydophila species. They also exibit an obligate biphasic intracellular life cycle within eukaryote host cells. Some of these new chlamydiae are currently considered potential emerging human and/or animal pathogens. Parachlamydia acanthamoebae and Simkania negevensis are both emerging respiratory human pathogens, Waddlia chondrophila could be a novel abortigenic bovine agent, and Piscichlamydia salmonis has recently been identified as an agent of the gill epitheliocystis in the Atlantic salmon. Fritschea spp. and Rhabdochlamydia spp. seem to be confined to arthropods, but some evidence for human exposure exists. In this review, we first summarize the data supporting a pathogenic potential of the novel chlamydiae for humans and other vertebrates and the interactions that most of these chlamydiae have with free-living amoebae. We then review the diagnostic approaches to infections potentially due to the novel chlamydiae, especially focusing on the currently available PCR-based protocols, mammalian cell culture, the amoebal coculture system, and serology.