Background: Individuals with type O blood have reduced factor VIII and von Willebrand factor levels compared to the non-O counterpart. Infusion of hydroxyethyl starch (HES) impairs coagulation and, in O blood type, apparent coagulopathy can develop after HES infusion. A newly market-released balanced HES (670/0.75) has physiologic pH and balanced electrolytes including calcium, which are beneficial to coagulation. Studies comparing balanced HES (670/0.75) with saline-based HES (130/0.4), previously known the least coagulopathic are rare. Therefore, we try to reveal the difference of coagulation, pH/electrolyte balance, and bleeding amount between the non-O and O blood types after infusion of these two newest HES.