The histochemical binding to normal and neoplastic human gastric mucosa of two lectin-peroxidase conjugates which are specific for fucose-containing glycoconjugates is described. The lectins are Ulex europaeus (UEA1) and Lotus tetragonolobus (LTA). Results are compared with ABO and secretor status and the immunohistochemical demonstration of a Type 1 antigen (Lewisa) and two Type 2 antigens (X and H) using monoclonal antibodies. Binding of UEA 1 and LTA to surface mucus cells in normal gastric mucosa is only seen in secretors but is independent of ABO status. In gastric carcinomas lectin binding is reduced. There is a relationship between UEA1 binding and the immunohistochemical demonstration of H Type 2 antigen and secretor activity. In contrast LTA staining is associated with both H Type 2 and Lea antigen but not with secretor status. X antigen is only demonstrable in small amounts. Despite subtle differences in the binding patterns of the two lectins, immunohistochemical studies with monoclonal antibodies against defined oligosaccharides provide greater information. The results of the study are consistent with the hypothesis that competitive interaction between fucosyl and sialyl transferases occurs in gastric malignancy and leads to the expression of abnormal blood group-related antigens.