This report describes the expression of glial and neuronal cytoskeletal proteins and their messenger RNAs (mRNAs) in established cell lines derived from human primitive neuroectodermal tumors (PNETs) and malignant gliomas. Northern blot analyses revealed neurofilament (NF) protein mRNAs in 6 of 7 PNET cell lines but no glial fibrillary acidic protein (GFAP) mRNA. Six of these cell lines contained mRNA for the microtubule-associated protein (MAP) known as MAP1b, whereas MAP2 mRNAs were detected only in 1 of the PNET cell lines. These findings closely paralleled previously published data on the expression of these cytoskeletal proteins in the same group of PNET cell lines. Although GFAP mRNA was detected in only 2 of 5 glioma cell lines, 4 of these cell lines contained mRNAs for the low-molecular-weight (M(r)) NF protein (NF-L). Western blot analysis confirmed the expression of both GFAP and NF-L protein in 2 of the glioma cell lines (U251 MG and U373 MG) that contained GFAP and NF-L mRNAs. Further, double immunofluorescence studies showed that GFAP and NF-L co-localized in the same glioma cells. In contrast, neither the middle- (NF-M) or high- (NF-H) M(r) NF proteins or their mRNAs were detected in any of these glioma cell lines. Finally, MAP1b mRNA was expressed in all 5 glioma cell lines, whereas MAP2 mRNAs were detected in only 3 of the cell lines. This is the first documentation of the expression of both glial-specific and neuron-specific cytoskeletal proteins in human malignant glioma-derived cell lines. These data may reflect the aberrant induction of neuron-specific gene products in some neoplastic glial cell lines. Alternatively, our findings may indicate that some glioma cell lines correspond to transformed bipotential human central nervous system precursors of cells restricted to a neuronal or glial lineage.