The chemical composition of lipopolysaccharides from Legionella erythra and Legionella oakridgensis was analysed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed both lipopolysaccharides to have a smooth-type character. The polysaccharide part of both lipopolysaccharides contained D-mannose, D-glucose, D-glycero-D-mannoheptose, L-glycero-D-manno-heptose, 2-keto-3-deoxyoctonic acid, L-fucosamine, D-glucosamine, and glucosamine phosphate. In addition, L-rhamnose, glycerol phosphate, and glucose phosphate were identified in the polysaccharide part of L. erythra lipopolysaccharide. The main sugar identified in the lipid A part of both lipopolysaccharides, 2,3-diamino-2,3-dideoxy-D-glucose, was found to be substituted with a complex fatty acid composition including at least 16 different amide-linked 3-hydroxy fatty acids. Both lipopolysaccharides contained nonhydroxy fatty acids and the uncommon 27-oxo-octacosanoic acid, 29-oxotriacontanoic acid, and 27-hydroxyoctacosanoic acid. The lipopolysaccharide of L. oakridgensis also contained 29-hydroxytriacontanoic acid. The dioic long-chain acids heptacosane-1,27-dioic acid and nonacosane-1,29-dioic acid were only present in the lipopolysaccharide of L. erythra.