Cell wall lipopolysaccharides (LPS) prepared from oxidase-positive Moraxella duplex and from oxidase-negative Micrococcus calco-aceticus (a presumptive moraxella) contained D-glucose, D-galactose, glucosamine, galactosamine, lipid A, ethanolamine, fatty acids, phosphate, and protein. The lipid A moieties prepared from the LPS fractions were composed primarily of hexosamines, ethanolamine, fatty acids, and phosphate with minor amounts of the other LPS constituents. The LPS from M. duplex and M. calco-aceticus had the same neutral sugar composition but differed markedly in their hexosamine composition. Galactosamine was the major hexosamine component of M. duplex; also present was an unidentified amino sugar and a small amount of mannosamine. In contrast, glucosamine was the major hexosamine component of M. calco-aceticus with a lesser amount of galactosamine and no mannosamine. The presence of galactosamine as the major component of the lipid A of M. duplex suggests that this fraction has a novel structure which differs from the poly-D-glucosamine 'backbone' structure assigned to lipid A. The fatty acid compositions of the lipid A from the two species were mutually similar and consisted mainly of hydroxylauric, hydroxymyristic, and C17-cyclopropane fatty acids. The LPS fractions of the two organisms studied resemble that of Neisseria catarrhalis and differ from those of the true neisserias.Peer reviewed: NoNRC publication: Ye