A polyphasic study was undertaken to determine the taxonomic status of six strains received as Streptomyces hygroscopicus. The strains had chemotaxonomic and morphological properties typical of members of the genus Streptomyces and formed distinct phyletic lines in the Streptomyces 16S rRNA gene tree. These strains were distinguished from one another and from phylogenetically close neighbours using a combination of phenotypic properties. The combined genotypic and phenotypic data showed that all six strains form distinct centres of taxonomic variation within the genus Streptomyces. The following novel species are proposed to accommodate the strains: Streptomyces aldersoniae sp. nov. (type strain DSM 41909(T) =NRRL 18513(T)), Streptomyces angustmyceticus sp. nov., comb. nov. (type strain DSM 41683(T)=NRRL B-2347(T)), Streptomyces ascomycinicus sp. nov. (type strain DSM 40822(T) =NBRC 13981(T)), Streptomyces decoyicus sp. nov., comb. nov. (type strain DSM 41427(T) =NRRL 2666(T)), Streptomyces milbemycinicus sp. nov. (type strain DSM 41911(T) =NRRL 5739(T)) and Streptomyces wellingtoniae sp. nov. (type strain DSM 40632(T) =NRRL B-1503(T)).