AbstractMedical devices in contact with blood have to be haemocompatible. In vivo haemocompatibility is mediated by the glycocalix ofthe endothelial cells lining the wall ofthe blood vessel. 1fthis lining is injured or a foreign surface is implanted the blood contacts the sub-endotheliallayers ofthe vessel wall/body foreign surface and adhere there. This adhesion leads to the activation ofblood cells, mainly of platelets (thrombocytes), vasoconstriction and the release oftissue fuctor. This release triggers the activation ofplasmatic coagulation. The main role in these processes plays the activation ofplatelets. Methods for evaluation and prevention of activation of platelets on foreign body surfaces are presented.