To investigate cytoplasmic alterations in cancers of the endometrium, monoclonal antibodies against H, A and B blood group substances and related lectins such as Ulex europaeus agglutinin 1 (UEA-1), Lotus tetragonolobus agglutinin (LTA), and Griffonia simplicifolia 1 (GS1-A4, -B4) were applied to 42 cases of endometrial adenocarcinoma (EAC) and 11 adenomyoses. The control specimens consisted of normal endometria with leiomyoma or adenomyosis from patients of known blood group type. The brightest and most consistent staining was obtained with GS1-A4, showing 98% positivity in EAC in contrast to 18% in normal endometria. In contrast, expression of A antigen was seen in only 24% of EAC and in 13% of normal endometria, UEA-1 binding was seen in 81% of EAC and in 10% of normal endometria, whereas H antigen was seen in 60% of EAC and 0% of normal endometria. In adenocarcinomas, staining was seen not only along the luminal border of glands but also in the cytoplasm and the lateral or basal cell membranes, whereas in the normal endometrium staining was mostly along the luminal border. Thus, a difference in the positivity and localization of glycoconjugates was observed in neoplastic and non-neoplastic endometrium.