Zorbamycin and its related antibiotics, zorbonomycin B and zorbonomycin C, are three new antibiotics isolated from fermentations of Streptomyces bikiniensis var. zorbonensis. All three antibiotics are active against a variety of Gram-positive and Gram-negative bacteria and various fungi. Zorbamycin as well as zorbonomycins B and C appear to belong to the phleomycin and bleomycin families of antibiotics and to be most closely related to the phleomycins. The three antibiotics described in this paper show differences from the reported phleomycins and are likely new members of this group. Culture of Streptomyces bikiniensis var. zorbonensis, grown in a complex medium, were found to contain a mixture of antibacterial agents which were characterized by their thin-layer chromatographic behavior. Since the bioactivity designated IV appeared to be one of the main components of the fermentation, we concentrated our efforts in isolating this material. Component IV was subsequently found to consist of three bioactivities. The main antibiotic was designated zorbamycin (U-30604E) while the two minor activities were named zorbonomycin B (U-32166E) and zorbonomycin C (U-33046E). The present communication deals with the production, isolation and chemical characterization of the three antibiotics. Results of preliminary in vitro testing of zorbamycin and both zorbonomycins B and C are also included in this paper. However, detailed discussion of the biological properties of these antibiotics will be the subject of subsequent communications.