Taxonomy of striped hamsters (Cricetulus barabensis group) is controversial.In particular,taxonomic treatment of the three closely-related chromosomal races ("barabensis" – 2n=20,pseudogriseus – 2n=24,and griseus – 2n=22) is disputable.Cytochrome B (Cyt b) gene sequence data showed that divergence between them (2-4%) falls close to the lower limit reported for interspecific level in rodents.We examined 462 specimens of the three karyoforms from 89 localities.The analysis of cyt b sequences demonstrated fragmentation into five allopatric phylogroups.Two of them correspond to "pseudogriseus" and "griseus" chromosomal races and are paired as sister groups.The "barabensis" race comprises three other branches and appears non-monophyletic.This phylogenetic arrangement suggests that the existing views on chromosomal evolution in striped hamsters may require revision.The most parsimonious scenario implicates two fission events while the traditional hypothesis postulates fusion of acrocentric chromosomes into metacentric ones.There are at least three zones of potential contact between races "barabensis" and "pseudogriseus" in Mongolia and Southern Siberia.Molecular and cytogenetic analysis of samples from these zones did not reveal regular gene flow between the races,although some evidence of rare hybridization events was found.The results of our laboratory cross-breeding experiments did not demonstrate effective reproductive barriers between any of the races.At present,no data on contact zones between "griseus" and the two other races are available.Therefore,the relationships of these taxa require additional examination.