Using labelled single copy DNA to cytoplasmic messenger RNA from a glioma cell line, it is shown by the excess RNA hybridization technique that a human glioma and a human fetal brain cell line both contain the mid and low abundancy classes of cytoplasmic messenger RNA. However, the high abundancy class present in the glioma cells is absent from the hybridization profile of the fetal cell line. Most of the nuclear RNA species complementary to this single copy DNA were present in the low abundancy class of both cell types; the mid-abundancy class was present in much lower concentration than in glioma cytoplasmic RNA and the high abundancy class was essentially absent. The extent of formation of S 1-nuclease resistant hybrids indicated that some of the messengers which are present in the high abundancy class in the cytoplasm of glioma cells are present in the lower abundancy classes of fetal brain cells. Thus the glioma cells appear to exhibit a higher degree of specialization potential than the embryonic cells.