Lectinlike adhesins were identified in the Bacteroides fragilis group by using sugars immobilized on agarose beads either with whole bacteria by direct microscopic examination or with soluble extracts by immunoaffinoelectrophoresis. These two methods allowed the identification of two sugars reacting with whole bacteria and with the corresponding extracts: alpha-D-glucosamine and D-galactosamine. Among eight strains tested representing seven species, the two strains of B. fragilis were equally adhesive and showed the greatest adhesions. The lectinlike adhesin was purified by affinity chromatography on glucosamine-agarose or galactosamine-agarose and showed one band at 70,000 daltons in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This lectinlike adhesin may help to elucidate the roles of the B. fragilis group in the colonization of intestinal surfaces and in the predominance of B. fragilis in infections alone and in synergy with other bacteria.