We cloned DNA fragments of sisomicin-producing Micromonospora inyoensis¹⁾ into Streptomyces plasmid vectors and identified Streptomyces lividans TK24 transformants expressing the M. inyoensis sisomicin-resistance (sisA) gene. The sisA gene was compared to the previously reported Micromonospora purpurea Kan-Gen (kanamycin-gentamicin)-resistance gene²⁾. While the restriction endonuclease digestion patterns of the two determinants appear to be divergent, the genes are nonetheless closely related, based on similar patterns and levels of aminoglycoside-resistance and their ability to cross-hybridize under stringent conditions. We have transformed recombinant plasmid pMD5-2, which carries the sisA gene, into our M. purpurea gentamicin-production strain and determined that gentamicin biosynthesis was not improved.