DNA samples from 21 unrelated Japanese patients with Duchenne muscular dystrophy (DMD) with nondeletion-type abnormality in the dystrophin gene and three samples from possible deletion carriers were analyzed using pulsed-field gel electrophoresis (PFGE). Among the 21 patients, 7 were found to carry partial duplications of the dystrophin gene spanning 50-400 kb. Of these 7 patients, 4 carried duplications corresponding to the major hot-spot regions for deletions (7.5-8.5 kb from the 5' end of cDNA), whereas two cases contained duplications in a region about 10 kb from the 5' end of cDNA, where causative mutations are reported to be rare. Only 1 case was found to contain a duplication of a region about 1 kb from the 5' end of cDNA, which is the reported duplication prone region. A combination of Southern blot analyses of conventional agarose gel electrophoresis and PFGE was confirmed to be useful, not only for detecting duplications and deletions, per se, but also for identifying carriers in the affected family.