Heparins are currently the anticoagulants of choice in long-term hemodialysis (HD). Because of their shortcomings, including the increasing incidence of heparin-induced thrombocytopenia (HIT II), osteoprosis, skin necrosis, hypersensitivity and hypoaldosteronism alternative anticoagulant is necessary. Direct-acting antithrombins, such as r-hirudin and its analogs have several potential advantages over heparin. They do not require a cofactor such as antithrombin111 (AT III), they are active against clot-bound thrombin and they have no known natural inhibitors, such as platelet factor 4. The aim of this prospective study was to provide safe and effective HD by investigating an appropriate PEG (polyethylene glycol)-Hirudin dosage regimen in patients on HD, as well as to compare the safety, tolerability and efficacy of PEG-Hirudin with that of unfractionated heparin (UFH).