Using immunochemical and immunohistochemical methods, the binding site of Anguilla anguilla agglutinin (AAA) was characterized and compared with the related fucose-specific lectin from Ulex europaeus (UEA-I). In solid-phase enzyme-linked immunoassays, the two lectins recognized Fuc alpha 1-2Gal beta-HSA. AAA additionally cross-reacted with neoglycolipids bearing lacto-N-fucopentaose (LNFP) I [H type 1] and II [Le(a)] and lactodifucotetraose (LDFT) as glycan moieties. UEA-I, on the other hand, bound to a LDFT-derived neoglycolipid but not to the other neoglycolipids tested. Binding of AAA to gastric mucin was competitively neutralized by Le(a)-specific monoclonal antibodies. UEA-I binding, on the other hand, was reduced after co-incubation with H type 2- and Le(y)-specific monoclonal antibodies. According to our results, AAA reacts with fucosylated type 1 chain antigens, whereas UEA-I binds only to the alpha 1-2-fucosylated LDFT-derived neoglycolipid. In immunohistochemical studies, the reactivity of AAA and UEA-I in normal pyloric mucosa from individuals with known Lewis and secretor status was analysed. AAA showed a broad reaction in the superficial pyloric mucosa from secretors and non-secretors, but AAA reactivity was more pronounced in Le(a+b-) individuals. On the other hand, UEA-I stained the superficial pyloric mucosa only from secretor individuals. A staining of deep mucous glands by the lectins was found in all specimens. Both reacted with most human carcinomas of different origin. Slight differences in their binding pattern were observed and may be explained by the different fine-specificities of the lectins.