In the course of systematic screening for new antibiotics, a strain of Streptomyces was isolated, which in submerged culture, produces a new antibiotic, glebomycin, belonging to streptomycin class. The antimicrobial activity of this antibiotic is characteristic of that of streptomycin: Streptomycin-dependent E. coli grows well around a paper disc containing glebomycin, and complete cross-resistance is observed between glebomycin and streptomycin or dihydrostreptomycin on a resistant strain of E. coli. Cysteine does not affect the antibacterial activity of glebomycin. The color reaction of Sakaguchi for the guanidyl radical is positive, but glebomycin does not form maltol on alkaline hydrolysis. The antibiotic was differentiated from other streptomycin-group antibiotics by paper chromatography and other physicochemical and biological properties. One of the significant characteristics of this antibiotic is its extremely low toxicity. This paper deals with the production and biological properties of glebomycin. The isolation and physicochemical properties of the antibiotic²⁾ and the taxonomic studies of the producing strain¹⁾ will be reported in companion papers.