SINCE the isolation of Streptomyces rimosus1, a number of other species have also been described which produce the antibiotic oxytetracycline. The status of some of these species has been questioned2,3, and comparative studies on induced mutants of S. rimosus4 suggest that other members of this group might be naturally occurring variants. One recently described species, S. albofaciens5, however, was stated to be distinct from S. rimosus as it produced a white aerial mycelium bearing numerous sporophores with monoverticillate spirals. The morphology of the sporophores is considered to be an important diagnostic character in the study of this genus, and if this culture falls into the section Monoverticillus–Spira of the scheme proposed by Pridham et al.6 it would be far removed from S. rimosus and might even be placed in the separate genus Streptoverticillium Baldacci7.