SPECT using Tc-99m MIBI was performed in patients with brain tumors in order to determine Tc-99m MIBI uptake in brain tumors and to evaluate the efficacy of MIBI imaging in the assessment of treatment response. A MIBI uptake index was calculated on SPECT imaging. All tumors with a MIBI-index higher than 7.5 were malignant. In the tumors evaluated before and after radiochemotherapy, the MIBI-index immediately following therapy correlated with treatment response 2 months after therapy. Thus, semiquantitative assessment using Tc-99m MIBI SPECT imaging may be useful in the evaluation of treatment response.