Hypertension and cerebral hyperperfusion are often seen in the immediate postoperative period after craniotomy for supratentorial tumours. This study was performed to evaluate the effect of ketanserin, given at the end of the peroperative period, upon cerebral blood flow (CBF), and cerebral metabolic rate of oxygen (CMRO2) before extubation. Mean arterial blood pressure (MABP), cerebral arterio-venous oxygen content difference (AVDO2), PaO2, and PaCO2 were repeatedly measured during the operation, and 180 minutes after extubation. Ten patients were included in this study. The results were compared to those from a recent study in which ten patients served as control. All patients were anaesthetized with thiopentone, fentanyl, nitrous oxide 67%, halothane 0.5% anesthesia. Ten patients were given ketanserin 10-20 mg (mean 18.5 mg) before extubation. There was no significant difference in CBF- and CMRO2 values between the two groups. During the period between closure of the dura and 5 minutes after extubation, an increase in MABP was observed in the control group (P < 0.05) but not in the ketanserin group. During the same period, a decrease in AVDO2 was observed in both groups (P < 0.05) and during the next 10 minutes an increase was observed. However, no difference in AVDO2 values between the two groups was found. These findings suggest that peroperative treatment with ketanserin reduces postoperative hypertension without influencing the cerebral blood flow or metabolism.