Hydroxyethyl starch (HES) is a frequently used plasma substitute that is popular due to a high degree of therapeutic safety. However, the administration of large volumes of highly substituted, high-molecular-weight starch often leads to iatrogenic von Willebrand syndrome (vWS) with hemorrhagic complications. In patients with cerebral circulatory disturbances we carried out hemodilution therapy during 9-10 days, infusing HES 200/0.62. A von Willebrand factor (vWF) multimeric analysis was carried out in 6 patients using a modified western blot according to the sodium dodecyl sulfate agarose gel electrophoresis method. The vWF multimeric analysis showed that all multimers decreased to the same degree, corresponding to type-I vWS.