We were unable to demonstrate the presence of the classic enterobacterium-type lipopolysaccharide in the cells of the Lyme disease spirochete, Borrelia burgdorferi B31. This finding was primarily based on chemical analysis and the absence of free lipid A upon mild acid hydrolysis of the appropriate cell extracts. These results do not preclude the possible existence of an unusual lipopolysaccharide-like compound(s) in B. burgdorferi.