Acetomycin was first reported by Prelog and coworkers as an antibacterial agent isolated from Streptomyces ramulosus, strain ETH 17633. This natural product has been subsequently found in culture of Streptomyces ramulosus Tue-32. The stereochemistry and absolute configuration of acetomycin was established by X-ray crystallography carried out in our laboratories on the antibiotic itself and elsewhere on a bromo derivative.