Cerebral pathology may alter the cerebrovascular reactivity to carbon dioxide (CO2). In the present study, in patients with brain tumors, we examined the cerebral vascular reactivity to CO2 in the cerebral hemispheres with and without tumors under intravenous and inhalational anesthesia. Twenty-nine patients undergoing craniotomy for frontotemporal gliomas were randomized to receive intravenous anesthesia with propofol or inhalational anesthesia with isoflurane. Cerebral blood flow velocity in the middle cerebral artery (VMCA) and pulsatality index were measured under normocapnia and hypocapnia in the normal cerebral hemisphere and the hemisphere with tumor. Hypocapnia significantly decreased the VMCA in both the cerebral hemispheres under both the anesthetic techniques (P<0.006). The percentage change in VMCA was similar between the hemispheres with and without tumor both under isoflurane (3.45±4.11% on the normal side and 2.91±2.40% on the tumor side; mean difference 0.54±1.31%; 95% CI -2.18 to +3.27) and propofol anesthesia (2.32±2.64% on the normal side and 1.69±4.04% on the tumor side; mean difference 0.63±1.2%; 95% CI -1.83 to +3.10). The changes in pulsatality index also were not significantly different between the hemispheres. In conclusion, cerebrovascular response to hypocapnia is similar between the normal and the abnormal cerebral hemispheres both under intravenous and inhalational anesthesia.