Hemodialyzed patients with increased risk of bleeding can be dialyzed according to a method of limited anticoagulant use including saline flush technique, regional citrate anticoagulation, regional heparinization or use of membranes with low thrombogenic properties. Methods that limit anticoagulation use are not completely effective, increase work load for the dialysis team and create a risk of complications. The aim of the study was to evaluate the clinical usefulness of Nephral ST dialyzers with poli-acrylonitrile membranes treated with polyethylenimine binding heparin in hemodialyzed patients with increased risk of bleeding. In 12 patients with increased bleeding risk, 121 hemodialyzed sessions were performed utilizing Nephral ST dialyzers. Heparin was not administered during the procedure. Degree of clotting of the dialyzer and the venous drip chamber was evaluated using a 4-degree visual scale. Platelet count, partial activation time of thromboplastine (APTT), thrombin time (TT), antithrombin III, as well as d-dimer concentrations were measured before dialysis and after 15, 120 and 240 minutes of procedure. No complications of massive clotting necessitating premature termination of dialysis was noted. In most sessions trace or small clotting was observed in the dialyzers and drip chambers. No significant differences in platelet count and AT III levels were measured. Increased TT and APTT after 15 minutes of dialysis were observed, which was probably due to release of small amounts of dialyzer membrane heparin. After 120 and 240 minutes these values returned to normal ranges. These observations along with increased d-dimers after 240 minutes suggested an increased risk of clotting during evaluated sessions. Application of Nephral ST dialyzers permits for heparin-free dialysis procedure in patients with increased risk of bleeding.