To determine whether tumor necrosis factor is of potential value for the treatment of human malignant gliomas, we studied the effects of human recombinant tumor necrosis factor (rTNF-alpha) on the morphology, incorporation of tritiated thymidine, and proliferation of 5 established cell lines derived from human malignant gliomas and 3 normal human brain cell cultures. A radioreceptor analysis for rTNF-alpha was performed on all cell lines and cultures. Two of the 5 human glioma cell lines (SF-188 and U 343 MG-A) demonstrated a marked decrease (60% or less of untreated controls) in the uptake of tritiated thymidine when treated with rTNF-alpha at a concentration of 40 U/ml; rTNF-alpha at 100 U/ml had antiproliferative and cytotoxic effects on both cell lines. The growth and proliferation of cell lines SF-126 and U 251 MG were not affected by rTNF-alpha even at high concentrations (5,000 U/ml). The growth and proliferation of SF-539 were affected to an intermediate degree. A colony-forming efficiency assay corroborated the results of the proliferation studies: SF-126 was relatively resistant (surviving fraction of 0.9 at 500 U/ml) and SF-188 was relatively sensitive (surviving fraction of 0.08 at 500 U/ml) to the cytotoxic effects of rTNF-alpha. Time-sequence electron microscopy showed that rTNF-alpha at a concentration of 500 U/ml caused ultrastructural changes in SF-188, including increased intracytoplasmic vesiculation, swelling and degeneration of mitochondria, loss of cell:cell junctional complexes, and fragmentation of the plasma membrane. Studies with 125I-rTNF-alpha showed a variable degree of binding in all cell lines and cultures. SF-188, a highly sensitive cell line, demonstrated the strongest binding of 125I-rTNF-alpha (3,400 receptors/cell with high affinity; kd = 0.27 nM), while SF-126, a highly resistant cell line, had the weakest binding (809 receptors/cell; kd = 0.25 nM). We conclude that there is a spectrum of antiproliferative and cytotoxic activity among glioma-derived tumor cell lines exposed to rTNF-alpha. An increased number of rTNF-alpha receptors appears to be a necessary but insufficient condition to explain the antiproliferative effects observed in some glioma-derived cell lines.