Background: Cerebral vascular spasm is the main complication of intracranial aneurysm during perioperative period. Anesthesia of clamp operation of intracranial aneurysm not only meet the basic requirement of anesthesia, but also prevent cerebral vascular spasm and protect cerebral function possibly. Objective: To observe the changes of angiot ensin II and endothelins of paitents with intracranial aneurysm under the anesthesia of desflurane during the clamp operation so as to discuss the effect of desflurane on cerebral protection. Design: Case analysis. Setting: Department of Ne urosurgery and Departm ent of Anesthesiology of Beijing Tiantan Hospital Affiliated to Capital University of Medical Sciences. Participants: Totally 64 patients, 30 males and 34 females, w ho were prepared for clamp operation of intracranial aneurysm, were selected from Department of Neurosurgery of Beijing Tiantan Hospital Affiliated to Capital University of Medical Sciences between October 2002 and June 2004. Methods: After anesthesia induction, tracheal cannula was used to control respiration and desflurane was used to maintain the anesthesia. Totally 4 mL arterial blood were collected at the four time points: before anesthesia induction, cutting dura mater, clamp aneurysm and 30 minutes after clamp aneurysm. Levels of angiotensin II and endothelins in plasma were assayed with radioimmunoassay. Main outcome measures: Le vels of angiotensin II and endothelins at the four time points: before anesthesia induction, cutting dura mater, clamp aneurysm and 30 minutes after clamp aneurysm. Results: Aneurysm of two patients was disrupted during the operation and other 62 entered the final analysis. 1 Level of angiotensin II: Level of angiotensin II was ranged normally before operation, and that at the other three time points during the anesthesia of desflurane did not changed obviously as compared with that at pre-anesthesia (P > 0.05). 2 Level of endothelins: Level of endothelins at the three time points of cutting dura mater, clamp aneurysm and 30-minutes after clamp aneurysm was lower than that at the time point of pre-anesthesia induction [(40.4±10.3), (40.0±9.6), (40.7±12.3), (49.3±12.7) ng/L, (P=0.002, 0.001, 0.009)]. Conclusion: Levels of angiotensin II and endo thelins which anesthetizes by desflurane are not increased during the whole clamp operation of intracranial aneurysm. However, level of endothelins is obviously lower than that at the time point of pre-anesthesia induction, and there is not significantly different from that at various time points of the operation. This suggests that anesthesia of desflurane can avoid the onset of acute cerebral vascular spasm induced by the increasing liberation of angiotensin II and endothelins and decrease the onset of secondary cerebral ischemic injury so as to protect brain.