A patient with glioblastoma multiforme (GBM) who had failed conventional therapy was treated with IL-2 gene therapy. The patient received 10 subcutaneous immunizations with autologous tumor cells and fibroblasts genetically modified to secrete IL-2 by retroviral gene transfer. An antitumor immune response mediated in part by CD8+ cytotoxic T cells was demonstrated with the patient's peripheral blood mononuclear cells. A magnetic resonance imaging (MRI) scan performed 4 weeks after the highest treatment dose revealed marked tumor necrosis. These results support the evaluation of this form of IL-2 gene therapy in additional patients with glioblastoma.