Abstract In addition to istamycin A and B previously isolated from culture filtrates of Streptomyces tenjimariensis, istamycin C, A0, B0, C0, A1, B1, C1, and A2 which contain the 1,4-diaminocyclitol moiety, have been found as minor components. Isolation and structural elucidation of these antibiotics are described. Istamycin A0, B0, and C0 are deglycyl derivatives, and istamycin, A1, B1, and C1 are 2″-N-formyl