The C-2-symmetrical phenazines produced by Microbispora and Streptosporangium were identified as 1,6-phenazinediol-5,10-di-N-oxide (phi d-dioxide) and 1,6-phenazinediol (phi-diol). Both oxidation of phi-diol to phi d-dioxide and reduction of phi d-dioxide to phi-diol were detected with M. amethystogenes and M. parva. No albino mutants lacking phi-diol-oxidation ability were isolated from cultures of Microbispora incubated in the presence of acridine orange, or those incubated at sublethal temperatures.