The lipopolysaccharide of Serratia marcescens, under mild hydrolysis conditions (0.25\u2002N H2SO4 for 2.5\u2002h at 100\ub0), yielded a lipid A containing D-glucosamine, fatty acids, acetyl and phosphate groups (approximate molar ratio 3:9:4:2), a small amount of ethanolamine, and a trace of galactosamine. Lipid A on methylation and subsequent hydrolysis yielded 3,4-di-O-methyl-D-glucosamine and 3,4,6-tri-O-methyl-D-glucosamine identified by gas\u2013liquid chromatography as their glucitol acetates. These sugars were further identified by ninhydrin degradation to yield 2,3-di-O-methyl-L-arabinose and 2,3,5-tri-O-methyl-L-arabinose. From these findings, it was concluded that the D-glucosamine units in the lipid A were linked 1\u2002\u2192\u20026. A negative optical rotation of the lipid A suggested a \u3b2 linkage. On the basis of the glycosidic linkage evidence and additional compositional data, a possible structure for the lipid A of S. marcescens is proposed and discussed in detail.Peer reviewed: YesNRC publication: Ye