The object of this research is to study, in different in-vitro systems and in an appropriate animal tumor model, some of the phenomena pertaining to cell differentiation, tumor maturation and stroma-induction, as expressed morphologically, biochemically, and immunologically, in neoplasms of the central and peripheral nervous system. The tumors investigated include human neoplasms; experimental rat tumors obtained following transplacental ethylnitrosourea (ENU); an established glial rat tumor cell line (C-6); and the neuroepithelial component of a transplantable mouse testicular teratoma (OTT-6050) maintained in syngeneic animals in ascitic and in solid forms. Two main approaches are used: 1. The establishment of suitable organotypic culture systems that permit the sequential study of differentiation by morphologic, immunologic and immunoradiometric methods. Autoradiographic studies are being undertaken to determine the kinetics parameters applicable to these cultures, particularly in reference to the growth fraction that can be estimated in the steady-state regions of the explants. 2. The biological properties and in vivo and in vitro behavior and manipulation of the mouse transplantable teratoma as a model for neuroepithelial neoplastic differentiation. The interest of this model lies in its applicability to the study of embryonal central nervous system tumors in man. A long-term objective is the production of a pure experimental tumor in which differentiation is restricted to neuroepithelial derivatives. Markers of differentiation include those concerned with gliofibrillogenesis (GFA protein), cell surface membrane antigens specific for neuroepithelial cells, melanin production in association with primitive neuroepithelium, and the determination and quantitation of biogenic amines by high-sensitivity microspectrofluorometry.