~~~~~ ~~Streptomyces sp. strain C5, an organism that normally produces baumycins, daunomycin and E-rhodomycinone, was treated with N-methyl-N'-nitro-N-nitrosoganidine (NTG). Mutants blocked at various points in daunomycin and baumycin production were isolated by screening for altered pigmentation and absence of bioactivity against Staphyfococcus aureus. Examination of the mutants by thin-layer chromatography of their accumulated anthracycline metabolites, by cosynthesis assays, and by extract feeding experiments allowed a classification into six groups. These were: dauA, strains that accumulated no anthracyclines but with other blocked mutants cosynthesized anthracyclines (polyketide-synthase-minus mutants); dauG, regulatory mutants that, either alone or mixed with other blocked mutants, accumulated no anthracyclines; d a d , mutants that accumulated aklanonic acid; dauE, mutants that accumulated maggiemycin; dauF, mutants that accumulated aklavinone; and dauH, mutants that accumulated only E-rhodomycinone. Mutant SC5-24 (dauE), which accumulated the shunt product maggiemycin, was re-mutagenized with NTG to obtain blocked mutants in preceding biosynthetic steps; the three groups of double mutants obtained accumulated aklanonic acid (dauC,E), aklanonic acid methyl ester (dauD,E) and aklaviketone (dauE,F).