The peptide antibiotic globomycin was extracted from the culture filtrate of Streptomyces halstedii No. 13912, purified on silica-gel columns and crystallized from acetonitrile to give colorless needles. It is a neutral substance with m.p. of 115 degrees C and a molecular formula of C32H57N5O9. On amino-acid analysis, it gave serine, threonine, glycine and an unidentified amino acid. It is soluble in methanol, ethyl acetate and chloroform but sparingly soluble in water. The antimicrobial spectrum of globomycin revealed its specific activity against Gram-negative bacteria. Formation of spheroplasts was observed when Escherichia coli was grown in the presence of globomycin, indicating inhibition of the bacterial cell wall synthesis as its mode of action.