Abstract: Based on physico-chemical properties and analysis of spectra, zhengguangmycin A₆ was identified as bleomycin A₆. As reported in literature, the addition of a certain amine to the fermentation media increased the ratio of production of the bleomycin which contains the added amine as the terminal moiety. Spermidine (0.36 mg/ml) Was very efficiently incorporated into bleomyein A₅ and completely suppressed the production of other bleomycins. However, it is an exception for bleomycin A₆, which is present in natural bleomycins in only trace amounts, even after the addition of its terminal amine (spermine 0.30 mg/ml) to the fermentation media. But the amount of zhengguangmycin A₆ is different. Under normal conditions the amount of zhengguangmycin A₆ in natural zhengguangmycins is usually over 10%, in some batches, reaching 15% and was the second important component in an amount next to zhengguangmycin A₅ (pingyangmycin). This suggests that the producing strain of zhengguangmycins, Streptomyces verticillus var. pingyangensis nov. is different from that of bleomycin, S. verticillus.