This research is based on the hypothesis that important events in differentiation and cellular regulation occur at the cell surface and that these events are mediated by specific surface molecules. Differentiation- and tumor-related antigens of the nervous system are being recognized and defined through production of monoclonal-antibody reagents. The resulting reagents are being used as markers for tumor cells and subclasses of tumor types. They will also be used in analyzing the biological and biochemical events of nervous system differentiation and tumorigenesis.