An environmental Myeobaeterium able to degrade phenanthrene, pyrene and fluoranthene was transformed with an IS1096-based transposon marker system. Electroporation and subsequent delivery of the transposon enabled formation of constitutive lacZ transformants, with similar growth rates on pyrene and R2A media to the parental strain. A semi-selective medium was developed to recover and detect colonies of the transformed strain after inoculation into polycyclic aromatic hydrocarbon-contaminated soil. Microcosm experiments involving inoculation of the tagged Mycobacterium strain into a historically PAH-contaminated soil indicated survival when an appropriate carbon source was available. The results reported show that transposon systems developed for clinical mycobacterial isolates are also applicable for use in environmental isolates. The results also show that inoculated Mycobacterium strains could survive for at least 100 days at 10(6)-10(7) cfu g(-1) in the PAH-contaminated soil tested here.