✓ The humoral immune response to autologous gliomas has been investigated in 16 patients using immune adherence and anti-C3 immunofluorescence assays of serum samples. Significant antiglioma antibody activity was detected in 56% of these sera. Fractionation experiments demonstrated that IgM class antibodies were more effective than IgG in their ability to fix complement on cultured glioma cell membranes. In addition, autologous IgG was shown to inhibit IgM complement-fixing activity in some experiments. “Capping” of immune complexes on the glioma cell surface is also described.