Mouse chromosome X- and 7-specific DNA fragments have been isolated from a recombinant DNA library enriched for X(7) chromosome sequences. The library was enriched by flow sorting the X(7) chromosome, a derivation of the Cattanach translocation, prior to library construction. A DNA fragment was found to be located in a region deleted in newborn mice doubly heterozygous for the two albino deletions c3H and c6H in chromosome 7. These chromosome-specific DNA fragments will be useful for studying X inactivation spreading in the X-autosome translocation (T(X;7) 1 Ct) and for investigating the developmental effects of the lethal albino deletions.