Glycinothricin is a streptothricin-class antibiotic obtained for the first time from the culture broth of a strain of Streptomyces griseus. Glycinothricin, the deformimino derivative of antibiotic LL-AB664, gives N-methylstreptolidine, N-methyl-D-glucosamine and glycine on acid hydrolysis. In comparison with LL-AB664, glycinothricin is less active against gram-positive and gram-negative bacteria and less toxic to mice. A new streptothricin-class antibiotic, glycinothricin, was obtained from the fermentation broth of a streptomycete, strain No. 979, isolated from a soil sample collected at Noroshi, Ishikawa Pref., Japan. The antibiotic was isolated as an amorphous hydrochloride by the conventional method for isolation of basic water-soluble antibiotics. Glycinothricin is similar in structure to LL-AB664, but differs from it by the absence of a formimino group. This is the first time this antibiotic is reported as a fermentation product, though it was presumed to be formed by degradation of antibiotic LL-AB664.