A 32 kilobase-pair fragment of intron 7 of the human dystrophin gene has been sequenced and analysed for the presence of repetitive elements and open reading frames. Two transposon-like human elements (THE-1 sequences), and three intervening, and related, long terminal repeat elements, together with three Alu sequences and a LINE sequence have been identified. These represent an unexpected clustering of highly-repetitive sequences within this single segment of intron DNA. Amplification of a region of chimpanzee genomic DNA by the polymerase chain reaction has provided evidence that at least one of the THE-1 sequences is present in the same position in the chimpanzee genome and the high homology between the human and chimpanzee sequences indicates that this element was fixed within the ancestral genome before the divergence of the two species. The possible role of repetitive, transposon-like sequences in natural mutagenesis of the dystrophin gene is discussed.