The epithelial cell adhesion molecule Ep-CAM, which is also design atedtumor-associated calcium signal transducer 1 and MK-1, is a monomeric membrane glycoprotein that is expressed in most normal human epithelium and in most carcinomas. The human Ep-CAM gene encodes a 314 amino acid protein that is expressed as two forms, a 40 kDa major form and a 42 kDa minor form, which are reduced to 35 kDa upon treatment with the aminoglycosylation inhibitor tunicamycin. Ep-CAM is overexpressed in a variety of carcinomas and is, therefore, a potential target for the visualization and therapy of human solid tumours. Ep-CAM contains an extracellular domain containing two epidermal growth factor-like repeats, followed by a cysteinepoor region, which are necessary for the adhesion properties of the molecule.