Meningococcus is an aerobic, fastidious, Gram-negative diplococcus that is found only in humans. Its cell wall has a cytoplasmic membrane, a peptidoglycan layer, and an outer membrane. Meningococci isolated from the bloodstream or the spinal fluid are almost always encapsulated. The capsules are polysaccharides, which consist of repeating sugar units (1,2). The capsular polysaccharide can be isolated, purified, and chemically and physically defined. Based on the chemical and immunological specificity of its capsular polysaccharides, Neisseria meningitidis has been classified serologically into groups A, B, C, 29E, H, I, K, L, W135, X, Y and Z (2). Of these, groups A, B, and C are responsible for approx 90% of meningococcal meningitis, and group B meningococcus is responsible for the majority of meningococcal disease in industrialized countries (1,2). The structures of the repeating units of the meningococcal polysaccharides have been elucidated and are shown in Table 1. Table 1 Structures of the Capsular Polysaccharides of N. meningitidis Group Structure of repeating unit Reference A →6)α-D-ManNAc(1-PO4→ (8) 3 ↑ OAc B →8)α-D-NeuNAc(2→ (5) C →9)α-D-NeuNAc(2→ (5) 7/8 ↑ OAc H →4)α-D-Gal (l→2) glycerol 3-PO(4)→ (6) L →3)α-D-GlcNAc (l→3) β-D-GlcNAc (l→3) α-D-GlcNAc-1-PO(4)→ (7) X →4)α-D-GlcNAc-1 -PO(4)→ (4) Y →6)α-D-Glc (l→4) α-D-NeuNAc (2→ (OAc) (9) W135 →6)α-D-Gal (l→4) α-D-NeuNAc (2→ (9) Z →3)α-D-GalNAc (1→1) glycerol 3-PO(4)→ (10) 29E →7)β-D-KDO (l→3) α-D-GalNAc (l→ (11).