Over 20 females have been reported to carry reciprocal X; autosome translocations with breakpoints in Xp21 and to suffer from Duchenne muscular dystrophy (DMD). We have positioned nine of these breakpoints with respect to the Duchenne gene by mapping probes from the DMD region against a panel of somatic cell hybrids, each containing one of the translocation chromosomes from a different female patient; further information has also been obtained by in situ hybridization, including the breakpoint location in a tenth DMD patient. We have also characterized two translocation breakpoints that lie in the same chromosomal region but which are not associated with the expression of DMD. All the DMD-associated translocation breakpoints examined lie at several sites within the DMD locus and between the two non-DMD breakpoints.