We compared hypervolemic hemodilution (HVH) and isovolemic hemodilution (IVH) as means of perioperative blood conservation under standardized conditions. Thirty ASA status I/II adults slated for orthopedic, ear-nose-throat, or general surgery with expected blood loss of >500 mL underwent either IVH (n = 15) or HVH (n = 15). They were hemodiluted to a hematocrit (Hct) of 25% by blood withdrawal and simultaneous polygeline (Hemaccel((R))) infusion (IVH) or by infusing polygeline without blood withdrawal, thus creating hypervolemia (HVH). Further blood loss to a Hct of 20% was allowed before autologous/allogeneic blood transfusion to aim for a 24-h postoperative Hct of > or =25%. Systolic blood pressure (P = 0.0107) and central venous pressure (P = 0.0281) were significantly higher during HVH. The mean difference (MD) between the target postdilution Hct of 25% and the Hct achieved was not statistically significant in either group (MD [95% confidence interval; CI], 0% [-0.7% to 0.7%] for IVH and 0.6% [-0.1% to 1.3%] for HVH). The actual amount of allogeneic blood used was similar in the two groups, with an MD (95% CI) of -7 (-326 to 312), and was significantly less than the corresponding projected amount (MD [95% CI], -581 mL [-753 to -409 mL] in IVH; -376 mL [-531 to -221] in HVH). The two techniques were similar in time taken (MD [95% CI] = 7 min [-0.5 to 14.5 min]), cost incurred (MD [95% CI] = $1.7 (-$4.10 to $7.50]), and volumes of polygeline used (MD [95% CI] = -6 mL/kg body weight [-16 to 4 mL/kg body weight]). This study found IVH and HVH comparable in significantly reducing perioperative allogeneic blood requirements, time needed, and cost incurred. The formula used for achieving the desired HVH appears promising. CONCLUSIONS Both hypervolemic hemodilution (HVH) and isovolemic hemodilution (IVH) claim to reduce red blood cell loss during surgery by diluting the patient's blood. This study found both comparable in significantly reducing the exposure to bank blood in the perioperative period, the time needed, and the cost incurred. HVH, being simpler, because it does not involve blood withdrawal, appeared superior to IVH in the healthy adults studied. Larger studies are needed to substantiate the results.