We have evaluated using immunohistochemistry the expression of the type 2 chain histo-blood group precursorsN-acetyllactosamine (Lac), sialosyl-Lac (S-Lac) and binary-sialosyl Lac (DS-Lac) in epithelial cells of normal non-secretory, gestational and malignant human endometrial tissues (n=120). Staining was assessed in relation to genetic (ABO, Lewis blood group and secretor status), morphologic and hormonal factors (serum levels of estrogens). The staining pattern for Lac, S-Lac and DS-Lac showed great variation and was not related to blood group or the secretor status. Staining for Lac showed a limited distribution in both normal and malignant endometrium and was most frequenly found in gestational and atrophic endometrium. S-Lac was strongly expressed, but only infrequently as DS-Lac structures in normal endometrium. Staining for both S-Lac and DS-Lac was most widespread in proliferating endometria. Endometrial carcinomas showed an increased staining for DS-Lac and a varied, and in most cases a reduced, staining for S-Lac, a pattern like that previously found in secretory endometrium. Staining scores for S-Lac showed a weak correlation with serum levels of free estradiol. Thus, the increased expression of DS-Lac in contrast to S-Lac structures in endometrial carcinomas is probably unrelated to both hormonal and genetic factors and may be considered a ‘tumor-associated’ but not a tumor-specific change in endometrial cell glycosylation.