CELLULAR IMMUNE EFFECTOR mechanisms are implicated as potential therapies for malignant gliomas. We have examined the potential for anti-CD3-activated human peripheral blood-derived CD4+and CD8+T cells to induce lysis of human glioma cell lines in vitro, the mechanism of action of these cells, and the capacity of the glioma to inhibit the effect. We found that activated CD4+and CD8+T cell preparations containing less than 5% natural killer cells could induce significant lysis of the glioma cell line U251, as measured by an 18-hour, but not 5-hour, chromium-51 or lactate dehydrogenase release assay. This effect was not reproduced using recombinant tumor necrosis factor or inhibited with antitumor necrosis factor antibody. Anti-lymphocyte functional antigen-1 and anti-intercellular adhesion molecule antibodies also did not inhibit the effect. Glioma-derived supernatant could inhibit the proliferation of the T cells but not the cytotoxic effect. Human fetal astrocytes were also susceptible to the cytotoxic effect of the activated T cells. These results indicate that activated T cells can induce glioma cytotoxicity via a mechanism independent of tumor necrosis factor. The therapeutic potential of this effector mechanism will depend on its capacity to deliver these cells or their specific effector molecules to the tumor site or to augment the activity of such cells, which accumulate naturally in gliomas.