A major surface constituent of Echinococcus multilocularis adult worms, referred to as an EmA9 antigen, was immunoaffinity purified and identified as a high-molecular-weight glycoconjugate. Labeling studies using the monoclonal antibody MAbEmA9 indicated that this antigen undergoes a regulated expression during the development from the larval to the adult parasite. Chemical modification of carbohydrate by periodate oxidation resulted in a reduced reactivity with antigen-specific antibodies. Non-reductive beta-elimination of the purified molecule indicated the presence of O-linked glycans attached to threonine residues. Carbohydrate compositional analyses indicated the presence of N- and O-glycans with the ratio of carbohydrate to protein being 1.5:1 (w/w). N- and O-linked glycans were released by hydrazinolysis and analyzed as 2-aminobenzamide derivatized glycans by mass spectrometry together with HPLC and enzymatic sequencing. Novel linear O-linked saccharides with multiple beta-HexNAc extensions of reducing end Gal were identified. N-Linked glycans were also detected with oligomannose and mono-, bi-, tri- and tetra-antennary-type structures, most of which were found to be core-fucosylated. Taken together, the results indicate that the EmA9 antigen is a glycoprotein located at the outer surface of the adult E. multilocularis. The observation that the EmA9 antigen expression is developmentally regulated suggests an involvement of this glycoprotein in the establishment of the parasite in its canine host.