Three isoforms of neural cell adhesion molecule (NCAM) are produced by differential splicing of the RNA transcript from a single gene. The 135kDa isoform is the basic molecule which is glycosylated or sialylated to produce the mature species. NCAM has been implicated as having a role in cell-cell adhesion, neurite outgrowth, synaptic plasticity, and learning and memory. NCAM (CD56) is reported to express on most neuroectodermal derived cell lines, tissues, and neoplasms such as retinoblastoma, medullblastoma, astrocytoma, and neuroblastoma. It is also expressed on some mesodermally derived tumors such as rhabdomyosarcoma and also on natural killer cells.