Production of rubomycin and carminomycinone glycosides by the rubomycin-producing organism was studied with the help of labeled rubomycin and carminomycinone. It was found that both substances were glycoxylized by the rubomycin-producing organism with production of the respective antibiotics. Non-labeled methionine did not decrease incorporation of rubomycinone labeled in the O-methy1 group into rubomycin. It is supposed that the methoxylic group of the latter is incorporated into its structure at early stages of its production, for example at the stage of polyketomethylen. Carminomycinone, which may be considered as desmethylrubomycinone not glycosylated by methylation.