By mutation and strain improvement techniques idiotrophs of Micromonospora purpurea, the gentamicin-producing organism, were obtained which require an exogenous source of 2-deoxystreptamine in order to produce gentamicin. Streptamine incorporation afforded a mixture of 2-hydroxygentamicin C as a complex of essentially the C1 and C2 components whereas 2-deoxystreptamine when incorporated by the same idiotroph afforded the same mixture of C1, C2 and C1a gentamicins as the parent (m1) organism. The 2-hydroxygentamicin C complex exhibited broad-spectrum antibiotic activity with an in vitro potency less than that for the gentamicin C complex, but with greater activity against selected gentamicin C resistant organisms. The LD 50 (i.v.) in mice of the 2-hydroxygentamicin C complex indicated that it had approximately half the toxicity of the gentamicin C complex. 2, 5-Dideoxystreptamine affordeda C1, C2, and C1a mixture of 5-deoxygentamicins, which also had broad spectrum activity, and exhibited improved activity against several gentamicin-acetylating strains of resistant bacteria. The LD50 (i.v.) in mice of the 5-deoxygentamicin C complex indicated that it was about 2.5 times more toxic than the gentamicin C complex. Two derivatives of 2,5-dideoxystreptamine afforded the same mixture of 5-deoxygentamicins. 2-Epistreptamine upon supplementation to a broth containing growing cultures of these idiotrophs also produced antibiotic.