The Thomsen-Friedenreich (TF) antigen (or, more precisely, epitope; Gal beta 1-3GalNAc-) has been known for a long time as a pancarcinoma antigen. Here we report the immunohistochemical identification of this carbohydrate antigen in the human placenta. Paraffin-embedded placental and decidual tissues of the first, second and third trimester were incubated with different monoclonal antibodies (A78-G/A7 and HH8) directed against the TF-epitope and stained with an immunohistochemistry system. We found a strong expression of the TF-epitope in the first trimester of pregnancy. In addition, we identified an expression of the TF-antigen in the second trimester of pregnancy but only in a few cases a positive staining in the third trimester of pregnancy.