BACKGROUND Acute normovolemic hemodilution (ANH) is used in major surgery expected to be accompanied by excessive blood loss. Reducing the hemoglobin content may disturb cerebral oxygen balance. The aim of this study was to assess the effect of ANH on cerebral oxygen balance in patients subjected to brain tumor resection. METHODS Forty patients were randomly allocated into 2 groups (hemodilution and control). In the hemodilution group (HG), 1000 mL of blood was drawn and replaced with the same volume of HES 130/0.4 (6%, Voluven) colloid. In the control group (CG), no blood was drawn, and hemodynamics were stabilized using normal saline until allogenic blood was needed. Arterial and jugular bulb blood samples obtained after induction (basal, sample 1), 40 minutes after induction (or on completion of hemodilution, sample 2), after surgical hemostasis (sample 3), and just before extubation (sample 4) were used for the calculation of arterial-jugular oxygen content difference "Ca-jO(2)," cerebral oxygen extraction "CEO(2)," estimated cerebral metabolic rate for oxygen "eCMRO(2)," cerebral blood flow equivalent "CBFe," and jugular-arterial lactate difference "J-ALD" in both groups. RESULTS Jugular oxygen saturation "SjvO(2)", CEO(2), and J-ALD showed no significant difference when the 2 groups were compared at the corresponding time points and when the values obtained at different time points were compared with the basal value in the same group. In CG, "Ca-jO(2)" significantly decreased at the end of surgery and before tracheal extubation (P<0.003 and 0.002, respectively). In HG, it decreased after hemodilution, with P value of less than 0.032. eCMRO(2) was significantly reduced in CG 40 minutes after induction of anesthesia, at the end of surgery, and before tracheal extubation (P<0.021, 0.001, and 0.001, respectively). In HG, eCMRO(2) was significantly reduced at the end of hemodilution and at the end of surgery with P value of less than 0.005 and 0.034, respectively. CBFe was significantly increased in CG at the end of surgery and before tracheal extubation (P<0.005 and 0.022, respectively). It was also increased after hemodilution in HG (P<0.042). There were no significant differences in Ca-jvO(2), eCMRO(2), and CBFe between the 2 groups. CONCLUSIONS ANH and allogenic blood transfusion used in this study design were accompanied by comparable cerebral oxygenation parameters in patients subjected to brain tumor resection.