Four forms of mole rats with diploid numbers of chromosomes of S2, 54, 58, and 60, respectively, were found in Israel and the vicinity. The differences between the chromosome sets are due to whole-arm (Robertsonian) changes and pericentric inversions. The geographic distribution of the different forms is contiguous. Only a few hybrid individuals have been discovered. These chromosome forms are tentatively considered as sibling species, almost completely isolated by cytogenetic and possibly ethological mechanisms. The weak dispersal powers of mole rats may have-contributed to a rapid fixation of adaptive homozygous chromosomal changes.