Tweleve mutants which produced novel biosynthetic anthracycline metabolites were obtained from two anthracycline producers, rhodomycin-producing Streptomyces violaceus A262 and daunomycin-producing Streptomyces sp. D788. by mutagenic treatment. The seven mutants were precursor aglycone-accumulating ones and the five mutants were glycosidic intermediate-accumulating ones. Five anthracycline-nonproducing mutants were also isolated. Interspecific recombination between these two Streptomyces strains is other important means for obtaining a diserbale biosynthetic mutant if it is possible. However, it was found that no recombination occurred between them.