On dystrophin gene analysis by multiplex polymerase chain reaction (PCR), 76 of 130 (58.5%) Japanese patients with Duchenne muscular dystrophy had a deletion or duplication in genomic DNA. Of the remaining 54 patients who had no identifiable gene mutations, muscle biopsy tissue was available in 16 for RNA extraction. The full length of the coding regions of dystrophin cDNA was amplified in 10 fragments by reverse transcription nested PCR (RT-PCR). Five of 16 patients (31%) had dystrophin cDNA of abnormal size. One patient had a deletion, and two duplications that were not covered by multiplex PCR, one an exon-skipping of exon 51 caused by a 5' consensus splice site mutation of intron 51, and one 172 bp or 202 bp insertion in the cDNA between exon 25 and 26. Nested RT-PCR from the total RNA extracted from muscle biopsy was useful for screening patients who had no identifiable gene abnormality by multiplex PCR.