A mixture of the sulfate salts of basic glycopeptide antineoplastic antibiotics isolated from Streptomyces verticillus. Bleomycin sulfate forms complexes with iron that reduce molecular oxygen to superoxide and hydroxyl radicals which cause single- and double-stranded breaks in DNA; these reactive oxygen species also induce lipid peroxidation, carbohydrate oxidation, and alterations in prostaglandin synthesis and degradation.