The isolation of three low molecular weight, chemically related compounds from Streptomyces fermentation broths has been reported recently.2 One of these compounds (I) has been found to be identical with the antibiotic enteromycin (seligocidin), reported by Nakamura, Maeda, and Umezawa,3 and whose structure has been established by Mizuno.4 The other two compounds, U-15,774 (II) and U-22,956 (III), are new. Enteromycin and U-15,774 are produced by Streptomyces achromogenes, which also produces streptozotocin,5 while U-22,956 is produced by Streptomyces fervens var. melrosporus. In spite of the close chemical relationship of these compounds, U-15,774 (II) does not have antibacterial activity, while the other two are quite active against various bacteria. This paper discusses studies which establish that the structures of U-15,774 and U-22,596 are represented by the expressions II and III, respectively, and which more firmly identify the third compound as being enteromycin (I).