New antibiotics were isolated from the culture broth of the myxobacterium, Sorangium cellulosum, strain So ce 678. The antibiotics were active against Gram-positive bacteria and mammalian cells. They were named tartrolon A and B. Tartrolon B contains a boron atom. The boron binding region of tartrolon is identical with that of boromycin and aplasmomycin. In our screening program for secondary metabolites from myxobacteria, we found an inhibitor of Gram-positive bacteria. It was produced by Sorangium cellulosum, strain So ce 678, and turned out to be a macrocyclic ring composed of two identical halves. There were two components; one of them contained a boron atom. We propose the name tartrolon. In the following we report on the production and biological properties of the new compounds. The structure elucidation has been published elsewhere1}.