Cytoreductive surgery is accepted by many neurosurgeons to be the best treatment for patients with malignant gliomas. Resection of a contrast-enhancing lesion on a CT or MR image is a particularly common treatment, because observation of such lesions indicates the presence of viable tumor cells. We have used intravenous injection of fluorescein Na (0.2 cc/kg body weight) as a chemical probe for resection of malignant gliomas. Following this injection, the yellow-stained tumor is visible to the naked eye. For tumors located in an eloquent area, resection is performed at the surface of the yellow-stained tumor, or tumor debulking within the yellow-colored lesion is conducted until the resection surface becomes pale yellow. For tumors located in non-eloquent regions, suction of peritumoral white matter is also required. This procedure requires no special equipment and has wide applicability in resection of malignant gliomas.