The number of tacrolimus (FK506)-producing isolates has increased remarkably because of the clinical importance of tacrolimus as an immunosuppressant. However, the taxonomy of several of these isolates has not been studied. The taxonomic status of strain ATCC 55098(T), a tacrolimus-producing strain, was determined in this study. The genotypic, phenotypic and chemotaxonomic properties were consistent with the inclusion of strain ATCC 55098(T) in the genus Streptomyces. The 16S rRNA gene sequence of strain ATCC 55098(T) was determined and used to generate phylogenetic trees with corresponding sequences of the most closely related type strains (≥ 98 % 16S rRNA gene sequence similarity) of species of the genus Streptomyces. Strain ATCC 55098(T) formed a distinct phylogenetic branch adjacent to a cluster comprising Streptomyces fulvissimus NBRC 13482(T) and Streptomyces flavofungini NBRC 13371(T). However, morphological and physiological tests and DNA-DNA relatedness distinguished strain ATCC 55098(T) from its closest phylogenetic neighbours. On the basis of these results, strain ATCC 55098(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces tacrolimicus sp. nov. is proposed. The type strain is ATCC 55098(T) ( = CECT 7664(T)).