In the microbial conversion of anthracyclinones by baumycin-negative mutant of Streptomyces coeruleorubidus ME130-A4, baumycins (4'-substituted daunomycins1)) and other parental metabolites2) were found to be produced from exogenous aklavinone or e-rhodomycinone in the fermentation medium. Thus, these anthracyclinones or their derivatives have been shown to be the biosynthetic precursor of daunomycinone. In this paper, we report the bioconversion of [9-14C]- and [16-14C]-labeled aklavinones to daunomycinone by a baumycinnegative mutant via e-rhodomycinone.