The karyotypes of four Mus oubanguii and two Mus minutoides/musculoides were studied by Q-, G-, and C-banding, Ag-staining, and incorporation of distamycine A. The results permit some considerations about the karyotypes of these two species and suggest that the karyotypes of Mus oubanguii and Mus minutoides/musculoides have arisen from a common ancestral karyotype, the former through centric and tandem fusions first and then through pericentric inversions, the latter through centric fusions.