Thirty-four Duchenne and Becker muscular dystrophy families were initially ascertained from South Australia. These have been tested systematically with the DNA probes XJ1.1 and pERT87-15. DNA results from 21 informative families have been combined with results of CK testing. Pedigree analysis was carried out using the computer program LINKAGE to provide risk figures to potential female carriers. This simple approach separated potential carriers into low or high risk classes (familial cases) or low or moderate risk classes (isolated cases). No prenatal diagnoses were carried out. The detection of deletions in two probands out of 34 makes possible definitive prenatal diagnosis in those families. For the remaining families, prenatal diagnosis could only be offered in terms of a probability statement after linkage analysis. Risk figures presented from hypothetical pedigrees demonstrated that prenatal diagnosis by linkage usually provided reasonable reliability only where informative flanking markers are used.