Simple mucin-type carbohydrate structures, T, Tn and sialosyl-Tn, are regarded as general markers of carcinomas in several epithelial tissues as a result of incomplete synthesis with precursor accumulation. The structures have a very limited distribution in normal tissues and secretions, including saliva and salivary glands. The expression of simple mucin-type carbohydrate structures and ABH(O) variants was studied in paraffin-embedded and frozen tissue sections from 37 pleomorphic adenomas with associated normal parotid tissue, using immunohistology and a panel of MAbs with well-defined specificity for T, Tn, sialosyl-Tn, and blood group H and A variants hereof. The immature Tn and sialosyl-Tn antigen structures were expressed in the epithelial ductular structures of the tumors, whereas they were almost absent from normal parotid tissue, indicating aberrant glycosylation with accumulation of precursor structures. Furthermore, the tumors showed loss of A antigen. The prognostic significance of these results is discussed. The modified myoepithelial cells in periductular and solid areas expressed T and sialosyl-T antigens, similar to normal myoepithelial cells and basal cells. Thus these modified MEC seem to have retained their normal simple mucin-type glycosylation pattern, suggesting that T antigen may be used as a marker of MEC in salivary gland tumors.