The myxobacterium, Myxococcus virescens strain Mx v48 produced a family of at least 12 closely related antibiotics, the myxovirescins^***. At a concentration of 1 to 5 μg/ml, the main component, myxovirescin A, was bactericidal for many Gram-negative bacteria, in particular enterobacteria, and at 20 to 50 μg/ml it also inhibited some pseudomonads and Gram-positive bacteria. The antibiotics seem to interfere with cell wall synthesis. The molecular formula of myxovirescin A was C₃₅H₆₁NO₈. It is a new antibiotic.