Regarding oral biofilm aspects, there has been strong evidence for a microbiotic component in the etiol. of halitosis. Many oral microbiota have protheolytic and putative activity, but there have been no studies investigating the association of microbiota in oral biofilms with halitosis. The objective of this study was to determine species of oral microbiota in the periodontal area and dorsal part of tongue biofilm, and how their quant. amounts differ in halitosis patients. The clin. bacterial material from halitosis patients (altogether 98 persons, volatile sulfur compounds (VSC) on average 380 ppb) was taken from periodontal pockets and the dorsal part of the tongue for microbiol. diagnostics of anaerobic bacteria, using polymerase chain reaction (PCR) tests for the comparison of bacterial quantity. The study showed the primary etiol. factors of halitosis in Latvia, and offers possible versions of microbiol. diagnostics of halitosis. Even though the examination of halitosis patients and determination of VSC using a halimeter is tech. simpler and cheaper, the determination of etiol. factors and their combinations using microbiol. examination of clin. material with PCR tests are more precise. A characteristic ecol. niche of anaerobic bacteria is not only the anaerobic environment of periodontal pockets, but also the microbiota of the dorsal part of the tongue. Addnl., some anaerobic bacteria species (Porohyromonas gingivalis, Tannerella forsythia, Treponema denticola, Prevotella intermedia) in larger amounts are found on the microbiome of the tongue. Therefore, it is advisable to begin microbiol. diagnostics in halitosis patients with quant. diagnostics of Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia, Treponema denticola on the biofilm of the tongue coating.