CD15 (Lewis x), also known as stage specific embryonic antigen-1 (SSEA-1) is a trisacharide determinant (3-fucosyl-N-acetyllactosamine) expressed on several glycolipids, glycoproteins and proteoglycans of various cell types, e.g. granulocytes, mast cells, monocytes, macrophages, cells of gastric mucosa, nervous system or various tumour cells. There are several structural relatives of Lewis x, e.g. sialyl-Lewis x or sulphated Lewis x. Cells with high surface expression of Le (x) antigen exhibit strong self-aggregation, based on calcium-dependent Le (x) -Le (x) interaction. This process is involved for example in embryo compaction or in autoaggregation of teratocarcinoma cells. Sialyl-Le (x) and its isomer sialyl-Le (a) are ligands of selectins. CD15 expression has been extensively used to confirm diagnosis of Hodgkin´s disease.