Moyamoya disease is a rare progressive occlusive disease in the internal carotid arteries, along with the presence of an abnormal capillary network of vessels at the base of the brain. In moyamoya disease, the manitaining of cerebral perfusion and cerebral oxygen saturation are required to reduce complications of this disease including cerebral ischemia and cerebral hemorrhage. The authors measured regional oxygen saturation (rSO2) nonivasively by INVOS 5100 (Somanetics, USA) in patients with moyamoya disease who were scheduled for an encephalo-duro-arterio-myo synangiosis (EDAMS) operation. We therefore report our findings that deep breathing decreased rSO2 and oxygen, elevated blood pressure, and that the cerebral vasodilating drug increased rSO2.