DNA was isolated from a chinese hamster/mouse hybrid cell line containing a single mouse chromosome, the X-chromosome, and digested with a variety of restriction endonucleases known to cut mouse satellite DNA. After agarose gel electrophoresis and transfer to nitrocellulose, hybridisation was carried out to a radioactive mouse satellite DNA probe. In this manner the organisation of satellite sequences at an individual chromosome was determined. We have found that the organisation of centromeric satellite DNA sequences on the mouse X-chromosome differs from that of other chromosomes in the complement. The nature of the differences suggests features of evolution of highly repeated sequences within a karyotype.