Feldamycin, a new antibacterial agent, and nojirimycin, a previously described antibiotic have been isolated from cultures of Streptomyces ficellus. Feldamycin, C17H25N7O5, is an amphoteric compound which inhibits a variety of bacteria in vitro but is found to be ineffective in the treatment of experimental bacterial infections in mice. Nojirimycin (5-amino-5-deoxy-D-glucose) has been isolated previously from cultures of several species of streptomycetes.