The l,5-diyn-3-ene-containing antibiotics represented by esperamicin1'^ and calicheamicin3) are receiving increasing attention because of their extremely potent antitumor activity and unusual structures. A unique mechanism of action involving phenyl diradical formation has been proposed for this family of antibiotics4). These antibiotics show extremely strong inhibition of growth of Gram-positive bacteria, especially the recombination-deficient mutants such as Bacillus subtHis M45 strain. During the course of our continuing search for newantitumor antibiotics using B. subtilis M45, dynemicin A, a novel violet-colored antibiotic was discovered in the fermentation broth of a new Micromonospora strain. The antibiotic exhibits very potent antibacterial activity, especially against Gram-positive bacteria, and prolongs the life span of mice inoculated with P388 leukemia. Structural studies revealed that dynemicin A is a unique hybrid of an anthraquinone and an l,5-diyn-3-ene system. This communication describes the production, isolation, physicochemical properties, structure, and biological activities of dynemicin A.