Bordetella hinzii has recently been isolated from immunocompromised human hosts. The polysaccharides isolated from its endotoxin (lipopolysaccharide, LPS) were investigated using chemical analyses, NMR, gas-liquid chromatography/mass spectrometry and mass spectrometry by plasma desorption, matrix-assisted laser desorption/ionization and electrospray. The following structure for the O-chain-free LPS was deduced from the experimental results: carbohydrate structure [see text] Mass spectrometry and serology revealed that the O-chains were different from the homopolymer common to Bordetella bronchiseptica and Bordetella parapertussis strains and were composed of a trisaccharide repeating unit. Masses up to 8 kDa were obtained for native LPS molecular species.