Lectins and blood group antibodies were used to probe the surface structures of Campylobacter jejuni and Campylobacter coli. Of the 29 strains tested, there were distinct reaction patterns. The lectin-reactive and blood group antibody-reactive sites on the bacterial surface were distinguishable from the heat-stable (lipopolysaccharide) antigenic determinants. The interactions were strain specific. The reactive sites were stable with respect to culture media and passage and may be useful as additional markers for strain characterization.