Sequences of the RNase P RNA gene were investigated for the phylogenetic analysis of the genus Saccharomonospora. Aligned nucleotide sequences, determined from the PCR-amplified RNase P RNA gene of representative strains of the genus Saccharomonospora, displayed 94.2 +/- 1.3% interspecific variances. The intraspecific similarity value was 99.7-100% in all species tested. Saccharomonospora azurea K161T and 'Saccharomonospora caesia' K76T displayed identical RNase P RNA gene sequences in the region that was determined and Saccharomonospora sp. K180 showed sequences distinct from validly described species with a similarity value of 94.6 +/- 1.0%. The phylogenetic trees constructed by aligning the sequences either within the genus Saccharomonospora or with other Gram-positive bacteria were similar to the ones derived using sequences of the 16S rDNA gene. Advantageous features of this gene for application as a molecular phyletic marker are discussed.