The structure elucidation of myxovirescin A, a new 28-membered macrocyclic antibiotic, is described. Myxovirescin A was isolated from the fermentation broth of Myxococcus virescens strain v 48 and of various other species of gliding bacteria in the course of a screening program for antibiotics. It inhibits the growth of E. coli and other enterobacteria; preliminary studies on its mode of action indicate that it interferes with cell wall synthesis. The previously isolated antibiotic complex was separated into several closely related components by reversed phase chromatography using a methanol-water gradient. The structure elucidation of the main component, myxovirescin A, is reported here.