Streptomyces thioluteus is known to produce thiolut in, aureothricin, aureothin, 1,6-phenazinediol (1), 1,6-phenazinediol 5-oxide, and 1,6-phenazinediol 5,10-dioxide (iodinin). In our study of this organism we have encountered all of these metabolites as well as several new ones described here. Using previously described methods the chloroform extracts of washed cells and filtered beer from S. thioluteus fermentations were fractionated to give pure compounds which were then compared with authentic samples. Thus identified was 1-phenazinol (2), 2-amino-3H-phenoxazin-3-one (6), 6-methoxy-1-phenazinol (3), and 1,6-dimethoxyphenazine (4). Although 4 is a known compound and 3 has been made recently by the reduction of myxin, neither had been found before in nature. Two other phenazines, not identical with any known naturally occurring phenazines, were isolated in amounts too small for complete identification. Their intense yellow-orange color with sodium hydrosulfite solution showed that both had a carbonyl containing substituent in conjugation with the ring system. The ester resembled, but was not identical with, the methyl ester of phenazine-1-carboxylic acid (5). The phenol had an ultraviolet and visible absorption spectrum identical with that of griseolutic acid (1-hydroxymethyl-4-methoxyphenazine-6-carboxylic acid). The isolation of such a variety of substituted phenazines from one organism is unusual and suggests that all types of naturally occurring phenazines are biosynthesized from a common intermediate. S. thioluteus also produced a phenoxazinone which resembled 6 in color tests and spectra but was more polar. The mass spectrum molecular weight of 256 and important fragmentation products of M - H2O and M - CH2OH suggested the previously unknown structure, 7, 2-ethanolamino-3H-phenoxazin-3-one. This was synthesized in two steps from 2-hydroxy-3H-phenoxazin-3-one and found to be identical with the natural product. When the cell-extract residue was treated with hexane, then ethanol, the insoluble portion contained 3,6-dibenzylidene-2,5-dioxopiperazines. The major one, compound 8, recognized by its absorption at 338 mp and basic hydrolysis to benzaldehyde, was identical with an authentic sample. The minor one had an nmr band at δ 3.61 suggesting a methoxyl group. Therefore glycine anhydride, benzaldehyde, and anisaldehyde were condensed to give a mixture of 8, 9, and the dianisylidenedioxopiperazine. After separation, the previously unknown 9, 3-anisylidene-6-benzylidene-2,5-dioxopiperazine, was identical with the natural product. Phenazines 3 and 4 showed some weak antibacterial activity; dioxopiperazines 8 and 9 were inactive toward all microorganisms used.