Four clonal lines have been established in tissue culture from a transplantable tumor of cervical nerve-root induced transplacentally with ethylnitrosourea in an inbred BD-IX rat strain. One clone (RN-2) has several biochemical properties of the nervous system that led to its classification as a Schwann cell line, namely (a) the synthesis of the nervous system specific protein S-100, (b) a high specific activity of 2′,3′-cyclic nucleotide-3′-phosphohydrolase, an enzyme present in high specific activity only in glial cells, and (c) the presence of a basic protein related by immunological crossreaction, molecular size, and amino-acid composition to the encephalitogenic protein from beef brain myelin. Clone RN-2 has a high plating efficiency, a doubling time of about 20 hr, and a mean of 43 chromosomes of normal morphology. Clone RN-2 has also been inoculated subcutaneously into syngeneic rats and grown as a clonal tumor with good growth properties.