The structure of the O-polysaccharide of the lipopolysaccharide from a diarrheal strain isolated in Bangladesh was studied with sugar, and methylation analysis, NMR spectroscopy, mass spectrometry and partial acid hydrolysis. The strain was first designated as Hafnia alvei, but later found to be a possible new species in the genus Escherichia. Two different polysaccharides were detected, a major and a minor one. The structure of the major polysaccharide is given below, while the structure of the minor one was not investigated. .