Aminoglycoside-resistance genes (grm) were cloned from a gentamicin producer Micromonospora purpurea and a sisomicin producer Micromonospora rosea. The nucleotide (nt) sequences of both genes were determined and the similarity between them was very high (90.4% identity). In either case, the transcription start point was localised to about 11 nt upstream from the likely translation start codons of grm, which is expressed as a polycistronic transcript. In studies to be reported elsewhere, it has been established that the M. purpurea grm gene encodes a ribosomal RNA methyltransferase. Here, we confirmed that the similarity of the two genes exists not only at the structural but also at the functional level.