Three separate in vitro admixture experiments were accomplished with bleomycin and other common parenteral medications. Bleomycin was assayed by a radioimmunoassay procedure. Bleomycin was found to be compatible with a majority of drugs including the aminoglycoside antibiotics, the vinca alkaloid antineoplastics, the antimetabolite fluorouracil, several phosphate salt corticosteroids, diphenhydramine and the anticoagulant heparin sulfate. Incompatible admixtures include the acidic cephalosporin and penicillin-derived antibiotics, the antineoplastics, methotrexate, and mitomycin C, the sodium succinate salt of hydrocortisone as well as ascorbic acid (vitamin C).