Many proteins first identified in the nervous system were also found to be expressed elsewhere in the body. The text reviews some of these 'neuronal' markers and delineates intersections between nervous and non-nervous tissues on the structural and functional level. Examples are given for nuclear antigens, cytosolic, cytoskeletal and membrane bound proteins, neurotrophic factors and developmental antigens. Clinical aspects of the expression of neuronal antigens in cancer-like paraneoplastic syndromes of the nervous system and tumor invasion along and within peripheral nerves are discussed. The accumulated data indicates that expression of "neuronal" protein in tumors may promote proliferation, invasiveness and metastatic spread. The large spectrum of neuronal antigens expressed in cancer including voltage-gated ion channels and numerous neurotrophic factors reflects the continuity from neuronal to non-neuronal differentiation.