Myxothiazol (AB-Mx f16-1), a new antifungal antibiotic, is produced by the myxobacterium Myxococcus fulvus strain Mx f16. It is active against many filamentous fungi, and completely inhibits growth of Mucor hiemalis at a concentration of 2 micrograms/ml. The molecular formula of myxothiazol was determined to e C25H33N3O3S2.