The antifungal antibiotics lanomycin and gluco lanomycin were recently isolated from fermentation broths of Pycnidiophora dispersa1}. The structures of these compounds were reported in a previous paper in this issue2). The biosynthesis of the major metabolite (1) (Fig. 1), was of interest to better understand which precursors, if added to the broth, might increase the fermentation yield. We were also interested in attempting to alter the structure of the molecule by feeding unnatural precursors and a knowledge of the biosynthesis of the antibiotic was seen as a necessary first step. The biosynthetic origin of the carbon atoms of lanomycin was unambiguously determined by feeding experiments using 14C and 13C labeled precursors followed by measurement of incorporation, if any, by counting the radioactivity or by 13C NMR analysis of the isolated product. A C-H HETCOR experiment gave the unambiguous assignment of each of the resonances in the 13C NMR spectrum of lanomycin and this information allowed the determination of the enriched carbons from the 13C labeling experiments. These studies show that lanomycin is derived from six acetate units, methionine and glycine as depicted in Fig. 2.