T-lymphocyte subpopulations (Tg or “suppressor cells” and Tm or “helper cells”) in the peripheral blood of 16 patients with malignant intracranial gliomas were analyzed. The number of Tm-lymphocytes was very close to normal in both preand postoperative samples, whereas Tg-lymphocytes were significantly increased preoperatively (18.55 ± 1.11 vs. 12.72 ± 1.19, p < 0.001) and were still slightly higher than normal after operation and radiation treatment. These preliminary findings suggest a possible role of T-suppressor lymphocytes in the impairment of cell-mediated immunocompetence that has been observed repeatedly in patients with malignant gliomas.