The production, isolation, and some structural studies of an antifungal, antibacterial, and antiviral substance from cultures of Streptomyces hygroscopicus are described. This material, designated pantomycin, appears to be a polypeptide antibiotic with inclusion of fatty acids and carbohydrate residues. Amino acid analysis of pantomycin acid hydrolysates indicates that it contains threonine, serine, proline, glycine, alanine, valine, alloisoleucine, and an as-yet-unidentified amino acid which appears to be different from types encountered in proteinaceous materials. In addition to the aforementioned compounds, the antibiotic was shown to contain alpha-aminobutyric acid after hydrogenation. Analysis of ether extracts of the hydrolysate mixture indicated the presence of several fatty aicds; myristic, isotridecanoic, lauric, and undecylic acids. The amino and fatty acid composition of pantomycin is similar to the known antibiotic stendomycin. Pantomycin appears to also have at least one carbohydrate-like residue incorporated into its structure. The presence of carbohydrate was indicated by periodic acid-Schiff base staining of electrophoretic patterns as well as positive color formation in the phenol-sulfuric and Molisch tests, but the carbohydrate did not appear to be either a hexose or a pentose. The antibiotic, which appears to be dissociated in alcoholic solution, forms stable aggregates under aqueous conditons.