The lipopolysaccharide (LPS) of a galU mutant of Pseudomonas aeruginosa PA103, a serogroup O11 strain, was sequentially extracted with phenol-chloroform-petroleum ether (PCP) followed by hot phenol-water extraction of the bacterial pellet remaining after PCP extraction. LPS was found in both the PCP extract as well as in the water phase of the hot phenol-water extract. Analysis of the carbohydrate portion released by mild acid hydrolysis of both LPS preparations, both before and after removal of all phosphate groups by treatment with aqueous HF, was performed by glycosyl composition and linkage analyses as well as by NMR and mass spectrometric analyses. The results showed that the carbohydrate portion of these two LPS extracts contained the same structure: namely, alpha-GalN(Ala)-(1-->3)-alpha-(7-Cm)HepII-(1-->3)-alpha-HepI-(1-->5)-alpha-Kdo-(2-->. The oligosaccharide preparation from PCP-extracted LPS consisted of a variety of structures containing up to six phosphate groups present as mono-, pyro-, and possibly triphosphate, primarily located on the HepI residue with some molecules having a monophosphate on HepII. The oligosaccharide preparation from the hot phenol-water-extracted LPS contained a similar variety of structures, but with an additional structure in which HepI contained a PPEA group at O-2. In addition, PAGE immunoblot analysis of the crude cellular extract with anti-A-antibodies revealed the presence of A-band material in both PA103 and the galU mutant. The A-band material was purified and characterized by glycosyl composition and linkage analyses, as well as by NMR spectroscopy, which confirmed that the A-band rhamnan polysaccharide was present but not as typical LPS since lipid-A or LPS core oligosaccharide components were not detected.