Objective To observe the effects of acute hypervolemic hemodilution(AHH)with dif-ferent plasma substitutes on blood gas analysis and plasma electrolytes in neurosurgieal patients.Methods Sixty ASA Ⅰ-Ⅱpatients undergoing elective neurosurgery were divided into 3 groups(n=20 each)：voluven group(group V),polygeline group(group P)and lactated Ringer solution group(group R).After in-duetion of anesthesia the patients were randomized to receive 20 ml/kg of either 6% voluven,5% polygeline or lactated Ringer solution within 30 min.Blood samples were taken before(T1),immediately(T2)and 30 min after the end fluid infusion(T3)for determination of blood gas analysis including Hct and Hb,the plas-ma electrolytes.And during the hemodilution the heart rate(HR),mean arterial pressure(MAP) and central venous pressure(CVP) were continuously monitored.Results Group R was significantly lower in fluid ex-pansion rate than group P and group V,but there was no significant difference between group P.In the HH procedure three groups of patients MAP and HR maintained stable relatively,CVP increased signifieantly af-ter AHH compared with the baseline value before AHH in group V and group P(P<0.01).Compared with T1,plasma potasgium concentration significantly increased in group P in T3 and plasma sodium concentra-tion signitieantly increased in group V in T2(P<0.01),while plasma calcium concentration significantly de-creased in group V in T2(P<0.05).Compared with T2,plasma potassium oncentration signitleantly in-creased in group V and group P in T3(P<0.05 or 0.01).Compared with group P,plasma potassium con-centration decreased in group V in T2,while plasma calcium concentration significantly decreased in group V in T3(P<0.05).but they were still within normal range.Conclusions Voluven and polygeline are compa-rable in expanding blood volume and more efficient than lactated Ringer solution,hemodynamics is stable.Voluven and polygeline are small influence to the blood gas analysis and plasma electndytes,and safety han-dling in neurosurgical pafients.