The pathophysiological notions of hemodilution treatment of ischemic seizures with plasma expanders indicates the significance of microcirculation. Microcirculation disorders arise from the interrelations of hemodynamic, vascular, and hemorrheologic factors. It seems that hemodilution with hydroxyethyl starch reduces peripheral microcirculation disorders, thus inhibiting the development of cerebral edema. In the case of subarachnoid hemorrhage, the hemorrheologic factors deteriorate less severely when given antifibrinolytic treatment with Aprotinin. Simultaneous hemodilution with hydroxyethyl starch can counterbalance the already existing changes.