In general, certain amino acid residues in a heterodetic depsipeptide antibiotic are easily replaced by an analogous amino acid, e. g. methylproline in actinomycin and isoleucine in quinomycin. As previously reported by Yoshida, quinoxaline-2-carboxylic acid (QXA), the chromophore residue of quinoxaline antibiotics, was found to be an obligatory intermediate for the biosynthesis of these antibiotics by Streptomyces. These results led the authors to attempt to replace the chromophore of quinomycin by a structural analogue of QXA. In this communication, quinaldinic acid (QNA) was used as an analogue. Streptomyses 731-1, which was isolated from Streptomyces sp. 732 by a colony selection technique and produced exclusively quinomycin A (echinomycin), was used as a quinomycin producer. The cultural conditions were as previously described except that the synthetic medium contained sodium nitrate instead of ammonium nitrate. When QNA was supplemented into the medium at the time of inoculation at the concentrations given in Table 1, the synthesis of antibiotic was stimulated, maximal yield was attained with 1 mM of QNA.