The structure of the antibiotic althiomycin has been determined by a combination of chemical and physical methods. We wish to report the structure of althiomycin (1), a chemically-novel antibiotic produced in these laboratories by a strain of Streptomyces chartreusis. Products identical to althiomycin have been isolated by several other groups1~3), but an early chemical study did not yield the correct structure. After our work had been completed, UMEZAWA, et al., independently published the same structure for althiomycin.1)