To compare the molecular weights (MWs) of lipopolysaccharides (LPSs) from 30 Lior serotype reference strains and 17 clinical isolates of Campylobacter jejuni, we analyzed their migration rates by SDS-PAGE and the silver staining of the gel. LPSs from the serotype strains showed one band in the low-molecular-weight region of the gel as did those from R mutants of enterobacteria. Based on those from Salmonella minnesota R mutants, MWs of LPSs from C. jejuni strains were calculated to fall within a range of 3900 to 5300. Furthermore, in comparison of MWs of LPSs from the clinical isolates with those from the same serotype reference strains, six out of eight serotypes did not coincide each other. These results indicate that the Lior method is unrelated with the Penner method in the serotyping of C. jejuni.