Analysis of a new karyological material of mole voles Ellobius tancrei from a zone of high chromosome variation (Pamiro-Alai) in comparison with the data obtained 25 years ago showed a slight shift of the chromosome numbers on the western border of the Robertsonian fan due to the expansion of the area of forms with a low chromosome number. In the central part of the fan zone, the process of active hybridization of forms with different chromosome numbers, but not of the original forms, is still going on. Some problems of speciation on the basis of Robertsonian translocations are discussed.