A methicillin-resistant Staphylococcus aureus (MRSA) strain B-26, isolated clinically in Hiroshima University Hospital, is resistant to bleomycin together with kanamycin. In the present study, we analysed the nucleotide sequence of the 5.1-kb HindIII fragment containing the bleomycin- and kanamycin-resistance genes, which were previously cloned [Bhuiyan et al. (1995) Appl Microbiol Biotechnol 43: 65-69] from the chromosomal DNA of MRSA B-26. The present study found that the DNA sequence contains the duplicated target sequence (GATTAGAT) consisting of 8 bp for transposase and the entire nucleotide sequence of the plasmid pUB110, together with the sequence of inverted repeats (16 bp), designated IR-r and IR-1 in IS431 mec. The 8-bp duplication sequence, produced by the transposable element, was first found by us. We proposed that bleomycin resistance in MRSA B-26 is attributed to the IS431 mec-mediated integration of pUB110 into the chromosome.