Laboratory hybridization has been achieved between two partially sympatric species of jird, Meriones shawi (2n = 44) and M. libycus (2n = 44). The parental karyotypes differ by at least three autosomal rearrangements and a remodeling of the X chromosome. F1 hybrid karyotypes contain a haploid set derived from each parent, and the species origin of four chromosomes, including the X, can be identified. The FI females are fertile, whereas F1 males are infertile owing to completely or markedly diminished spermatogenesis. The F1 females backcrossed with M. shawi males are fertile and produce normal-sized litters with normal sex ratios; male progeny from this cross have normal spermatogenesis and are fertile. The F1 females backcrossed with M. libycus males exhibit reduced fertility, small litters and an absence of male offspring. The taxonomic status of M. shawi and M. libycus is evaluated with respect to the chromosomal and hybridization data, and the isolating mechanisms involved with speciation in Meriones ate considered.