Comparison of the first subunit of mitochondrial cytochrome C oxidase partial gene sequences belonging to Baikal endemic piscine leeches and phylogenetically close Palaearctic species revealed that two Baikal species have unique DNA sequences, which during their evolution have accumulated sufficient number of nucleotide substitutions to be a molecular species marker. In addition, the species inhabited Angara River has a significant genetic distance from the Baikal population, calling into question its species affiliation.