Experimental mouse burn wound model was employed to evaluate the relative efficacy of Pseudomonas aeruginosa lipopolysaccharide as a protectives immunogen. LPS was found to be highly immunogenic and protective. Immunization of the animals with three doses of LPS (0.01 Ug each) increased the mean lethal dose more than 20,000 fold. The level of protection against a live challenge was proved to be serotype dependent. The fold-protection obtained by LPS of one strain against live challenges of other strains was not more than 220-fold. A multivalent LPS vaccine evoked high levels of protection against different challenge strains of various serotypes.