Tn, sialosyl-Tn and T antigens are simple mucin-type carbohydrate antigens that may be expressed in human neoplasies due to alteration of the glycoprotein biosynthetic pathway. Utilising specific monoclonal antibodies (HB-Tn1, HB-STn1 and HB-T1), we have investigated the expression of these simple mucin-type carbohydrate antigens in large intestine of 8 human foetuses at early gestational age (9-10 weeks), obtained after therapeutic abortion. In all cases the expression of Tn antigen was mainly localised as a thin rim at the cell membrane and occasionally in the supranuclear region of epithelial cells, while sialosyl-Tn antigen was documented in some goblet cell vacuoles and occasionally in the cytoplasm of columnar cells. T antigen was not expressed in any case. These results indicate that Tn and sialosyl-Tn antigens are expressed as early as nine weeks of gestation, further supporting the notion that they may be considered as oncodevelopmental cancer-associated antigens in the large intestine.