We previously have reported that indium-111 labeled anti-glioma monoclonal antibody G-22 (111In-G-22) exhibits diagnostic potential against human glioma xenografts in athymic mice. Herein, we report the selective tumor localization of 111In-G-22 in patients with glioma. Five patients were administered an average of 2.2 mCi of 111In-G-22 whole IgG intravenously. No immediate or delayed side effects were attributable to 111In-G-22 injection. Serial gamma scintigraphy and single photon emission computed tomography (SPECT) were performed, and the distribution in the brain and intratumoral accumulation of 111In-G-22 were evaluated. CT and/or magnetic resonance (MR) images were performed simultaneously and these images were compared. In the case of malignant glioma, tumor-imaging was successfully obtained beginning at 6 h following injection with a maximum uptake tumor/brain ratio at 48 h. The distribution of 111In was selective. It predominantly accumulated in the biologically active areas of the tumor. Furthermore, the tracer uptake appeared to correlate with the histologic tumor grade. This confirms the G-22 monoclonal antibody specifically binds to biologically active and malignant glioma tissue, and tumor-imaging using 111In-G-22 may give support to the diagnosis of malignant glioma.