An artificial mycobacterial transposon was constructed by placing two copies of the insertion sequence IS900 flanking a kanamycin resistance gene into a non-(mycobacterial) replicating vector. Constructs were introduced into mycobacteria by electroporation and transposition events conferring kanamycin resistance were selected. Integration of IS900 into several genomic sites was analysed by Southern blotting and shown to involve both simple insertions and cointegrate formation, suggesting that IS900 can transpose by a replicative mechanism. Kanamycin resistance of IS900-integrated transformants was shown to be stable in the absence of selection.