The simple mucin-type carbohydrate antigens, Tn, sialosyl-Tn, and T, are tumor-associated antigens of adenocarcinomas. We evaluated by immunohistochemistry the expression of Tn, sialosyl-Tn (s-Tn), T, and sialosyl-T (s-T) antigens in normal nonsecretory, early gestational, and malignant human endometrium in relation to genetic (ABO/Lewis blood-type) and hormonal factors. The blood group status had no influence on staining. Tn and s-Tn antigens were infrequently demonstrated in normal nonsecretory endometria but showed an increased expression in adenomatous hyperplasias and endometrial carcinomas, which was unrelated to estradiol (E2) levels, grade, and stage. The T disaccharide was demonstrated infrequently in both normal and malignant endometrium. Staining for T antigen showed an inverse correlation to serum E2 levels. In contrast, s-T antigen showed a pronounced but varied expression in normal and malignant endometrium, and the expression of s-T antigen was positively correlated with E2 levels in serum. Our findings suggest a hormonal influence on expression of simple mucin-type carbohydrates in human endometrium. However, the accumulation of Tn and s-Tn antigens in malignant endometrial cells seem to be unrelated to both genetic and hormonal factors. Because s-Tn is also expressed by secretory endometria, only Tn antigen can be considered a "tumor-associated" antigen of endometrial tissue.