Eight Mus minutoides/musculoides from the Ivory Coast, eight M. setulosus from the Central African Republic, and seven M. mattheyi from Burkina Faso were analyzed cytogenetically. The results obtained were compared with those from M. setulosus of the Ivory Coast and M. oubanguii and M. minutoidesi musculoides of the Central African Republic in order to study the problem of interspecific phyletic relationships in the African Mus genus. Several data proved to be interesting. First, the centric translocation of the sex chromosomes, which characterizes all TR-type African mice, is species-specific in regard to the autosomal pair involved. Second, the almost total identity of the karyotype of M. mattheyi with the presumed ancestral karyotype confirms the hypothesis that 36 acrocentric chromosomes represent the ancestral karyotype of African mice. Third, intraspecific variability of heterochromatic zones in M. setulosus may represent a step in the isolation of a future new species. Finally, our results reveal a nearly perfect homology of the chromosome arms between the four species studied; this suggests a remarkable karyotypic homogeneity in the African Mus genus.