The lipid A component of Campylobacter jejuni lipopolysaccharides (LPSs) contains the same architectural principle as that found in other bacterial species; however, unlike the case with other bacterial species, the lipid A backbone of C. jejuni strains is composed of a phosphorylated β(1'– 6)-linked disaccharide containing 2,3-diamino-2,3-dideoxy-D-glucose and D-glucosamine as the major molecular species. Despite a backbone that differs structurally from that of classic enterobacterial lipid A, C. jejuni lipid A is antigenically similar to enterobacterial lipid A, and the respective LPSs have comparable endotoxic activities. Structural variability is greater in the core oligosaccharide than in lipid A of C. jejuni LPS. Nevertheless, the inner core oligosaccharides of C. jejuni strains share a common unique tetrasaccharide and also possess a trisaccharide that occurs in the inner core of other bacterial species. Ganglioside mimicry in the outer core is a common feature shared by a number of C. jejuni serotypes, but this mimicry is not conserved in all serotypes.