Some exometabolites produced by basic representatives of human anaerobic microflora were investigated, detected by gas chromatography - mass spectrometry (GC-MS). In vitro besides lactic acid Bifidobacterium and Lactobacillus generate substantial amounts of phenyllactic and p-hydroxyphenyllactic acids. Clostridium produced 2-hydroxybutyric acid and to a lesser extent lactic and phenyllactic acids. In contrast to С. perfringens, C. sporogenes generates substantial amount of phenylpropionic and p-hydroxyphenylpropionic acids and less p-hydroxyphenyllactic acid. С. perfringens produced minor amounts of 2-hydroxyglutaric acid. Bacteroids are potent producers of succinic and fumaric acids; they also contribute to production of significant portion of lactic acid. E. lentum generate lactic, phenyllactic and succinic acids and form a characteristic only for ones (from studied microorganisms) 2-hydroxyhexanic and 2-hydroxy-3-methylbutyric acids.