We have attempted to evaluate the clinical usefulness of hemodilution in intracranial operation. The studies were carried out on 10 patients undergoing operation for intracranial aneurysm. We performed hemodilution with Normodex and Rheomacrodex and removal of arterial blood through a cannulated radial artery and intraoperative autotransfusion with arterial blood. We observed mean arterial pressure, heart rate, hemoglobin, hematocrit, and arterial blood gas analysis after removal of arterial blood with hemodilution and autotransfusion and compared them to controls. There were no significant changes in arterial blood gas analysis. Hemoglobin and hematocrit values were significantly changed from controls after removal of arterial blood with hemodilution. Hemodilution methods served a very useful purpose and were safe procedures in intracranial aneurysm operation.