Information about specific genes specially of pathogenic mycobacteria could be used to unequivocally identify isolates of mycobacteria which are of clinical interest. Both eukaryotic and prokaryotic ribosomal RNA (rRNA) genes have been shown to comprise sequences which are conserved and others which are divergent. In the present study, rRNA genes from several cultivable mycobacteria including M. tuberculosis and armadillo derived M. leprae have been investigated. rRNA was isolated, made radioactive in vitro and then used to identify restriction fragments of DNA containing rRNA gene sequences. It was observed that restriction endonuclease patterns of rRNA genes are characteristic. By probing with homologous and heterologous rRNA probes, fragments hybridizing maximum with homologous probes could be identified and it appears that sequences flanking the rRNA genes are not identical. These fragments need to be further sequenced to identify the nucleotide sequences specific to rRNA gene cluster. It would also be necessary to analyse several isolates of each species including armadillo derived M. leprae before reaching any conclusions.