Lipopolysaccharides (LPS) from Legionella bozemanii serogroup 1 and Legionella longbeachae serogroup 1 were subjected to chemical analyses. The lipid A part of both LPSs contained 2,3-dideoxy-2,3-diamino-D-glucose as major constituents and D-glucosamine and glycerol as minor constituents of the sugar backbone structure. Both LPSs exhibited a very complex fatty acid composition. Twenty amide-linked 3-hydroxy fatty acids were detected in LPS of L. longbeachae, whereas seventeen were encountered in LPS of L. bozemanii. Both LPSs contained nine ester-linked nonhydroxy fatty acids and the unique long-chain fatty acids 27-oxo-octacosanoic acid, 29-oxo-triacontanoic acid, heptacosane-1,27-dioic acid and nonacosane-1, 29-dioic acid. SDS-PAGE showed that L. bozemanii produced smooth-form LPS, whereas L. longbeachae LPS was mainly of the R-type. Composition analyses were in accordance with these electrophoretic patterns. D-Quinovosamine and L-fucosamine constituted 80 mol% of the polysaccharide part of L. bozemanii LPS. Other sugars identified were D-glucosamine, D-mannose, D-glucose, L-rhamnose, D-glycero-D-manno-heptose, L-glycero-D-manno-heptose, 2-keto-3-deoxy-octonic acid and glycerol. The polysaccharide chain from LPS of L. longbeachae appeared to be shorter, but composed of the same sugars except L-fucosamine. Both LPSs contained glycerol phosphate and glucosamine phosphate and L. longbeachae LPS contained in addition glucose phosphate.