The 16S rRNA and gyrB genes of 22 Streptomyces strains belonging to the Streptomyces griseus cluster were sequenced, and their taxonomic positions were re-evaluated. For correct analysis, all of the publicly available sequences of the species were collected and compared with those obtained in this study. Species for which no consensus sequence could be identified were excluded from the phylogenetic analysis. The levels of 16S rRNA gene sequence similarity within the cluster ranged from 98.6 to 100% with a mean value of 99.6 �� 0.3%, and those of the gyrB gene ranged from 93.6 to 99.9% with a mean value of 96.3 �� 1.5%. The observed average nucleotide substitution rate of the gyrB gene was ten times higher than that of the 16S rRNA gene, showing a far higher degree of variation. Strains sharing 99.3% or more gyrB sequence similarity (corresponding to an evolutionary distance of 0.0073) always formed monophyletic groups in both trees. Through the combined analysis of the two genes, clear cases of synonymy could be identified and, according to the priority rule, the assertion of the status of Streptomyces setonii as a distinct species and the reclassification of Streptomyces fimicarius as a later synonym of S. setonii and Streptomyces albovinaceus as a later synonym of Streptomyces globisporus are proposed. Emended descriptions of S. setonii and S. globisporus are provided.