We wish to report the complete identification and synthesis of viosamine, 4,6-dideoxy-4-amino-D-glucose, isolated from the lipo-polysaccharide of C. violaceurn, NCTC 7911. This 4-aminosugar represents the first of a new class of carbohydrates isolated and identified from the special polysaccharides of bacteria. Further, we suggest that this class of carbohydrate may be of wide occurrence and importance, since, in addition to its presence in the lipopolysaccharide of C. violaceurn, the N,N-dimethyl derivative has been shown to occur in the antibiotic amicetin, and since the properties of viosamine indicate that it is identical with one of the new aminosugars isolated by Strominger as a thymidine diphosphate nucleotide conjugate (TDP-X2) from Escherichia coli B. Natural crystalline viosamine hydrochloride was isolated as previously described, m.p. 132-138° dec., [α]25° -9° initial → +21° (24 hr., c 1, H2O). Synthetic viosamine hydrochloride was prepared starting with methyl-6-deoxy-4-tosyl-α-D-galactopyranoside dibenzoate (I), m.p. 157-158°. Treatment with azide ion followed by reduction with platinum catalyst and saponification with barium hydroxide gave methyl-4,6-dideoxy-4-amino-α-D-glucopyranoside (II), m.p. 117-118°; +144° (c 0.85, H2O). The crystalline N-acetate III was prepared, m.p. 188-189.5°; [α]25° +151° (c 0.43, H2O). The free amine II and the N-acetate III were subjected to periodate studies to confirm their structure; II consumed 2 moles of periodate at a rate essentially identical with that of methyl-α-D-glucopyranoside. The N-acetate III consumed one mole of periodate at a much slower rate. Many attempts to hydrolyze the α-methyl glycoside II failed to give a crystalline product, as did the many attempts to convert the natural viosamine into its α-methyl glycoside. Hydrolysis of the α-methyl glycoside N-acetate III was successful, using 2.5 N hydrochloric acid for 6.5 hr. at 100°. Crystalline synthetic viosamine hydrochloride (IV) was isolated in 60% yield after cation exchange chromatography, m.p. 130-138° dec., [α]25° -12° (8 min.) → +20° (22 hr., c 0.76, H2O). The decomposition point and optical rotation data correspond with the natural material. The infrared spectra of the natural and synthetic material were superimposable and the Rf values were identical in three systems: 1-butanol-acetic acid-water (5:1:4), Rf 0.14; phenol-water (3:1), Rf 0.27; and 1-butanol-ethanol-water-ammonium hydroxide (5:1.4:3:0.1), Rf 0.44. The n.m.r. spectrum of the free aminosugar hydrochloride in deuterium oxide supported the gluco-configuration.