<jats:p><jats:bold>Metabolites of Microorganisms. Sulfur‐Containing Ansa Compounds of the Naphthomycin Type</jats:bold><jats:p>From a strain of <jats:italic>Streptomyces (Tü 2357)</jats:italic> in addition to naphthomycin A, 4 new yellow pigments were isolated and their structures determined by spectroscopic comparison with naphthomycin A. Whereas the naphthomycins D and E are simple derivatives of naphthomycin A, having OH and H, respectively, instead of Cl, the naphthomycins F and G contain an <jats:italic>N</jats:italic>‐acetylcysteine residue linked to the aromatic moiety by a thioether group. Degradations with O<jats:sub>3</jats:sub> yielded identical products from the naphthomycins A, D, F, and G, showing coincident configurations in parts of the molecules. Naphthomycin F shows some biological activity against gram‐positive bacteria and fungi, although much weaker than naphthomycin A. The naphthomycins D, E, and G are inactive against microorganisms.