The interaction of the antiserum against Burkholderia solanacearum ICMP 8110 cells with lipopolysaccharides from 19 strains of B. solanacearum differing in O-specific polysaccharide structure has been studied using ELISA. No correlation was found between the O-specific polysaccharide structure and serological activity of the lipopolysaccharide. Most of the lipopolysaccharides isolated from B. solanacearum strains (except for 4157, 767 and 7942) displayed cross-reactivity with the tested antiserum. These data indicate that the strain under study pertains to the same serogroup. It cannot be excluded that some nonidentified components in the O-specific polysaccharide structure are responsible for the serological activity of the lipopolysaccharide.