We performed a crossover study to compare the effects of different dialysis membranes on 20 patients with frequent dialyser clotting and requiring >5,000 units of heparin per dialysis session. Low-flux dialysers are C15NL (cellulose - Terumo) and E15NL (vitamin-E-coated - Terumo) while high-flux dialysers were F60 (polysulphone) and EE15NL (vitamin-E-coated - Terumo). Ten patients underwent dialysis for 2 months with C15NL then switched to E15NL for 2 months. Similarly, the other 10 patients were started on the high-flux dialyser F60 and then switched over to EE15NL for 2 months. The following parameters were measured at the beginning of the study, 2 weeks, 1 month and then at 2 months: hemoglobin, prothrombin time (PT), partial thromboplastin time (PTT), fibrinogen, protein C, protein S, antithrombin III (ATIII) and factor 12 activity. Dialyser clotting, heparin and erythropoietin requirements were assessed during each dialysis session. There was a significant reduction in clotting with E15NL in comparison to C15NL (22.8 +/- 17 and 44.1 +/- 22.8 (p = 0.0233), respectively). Similarly, heparin requirements were less in the vitamin-E-coated (E15NL) dialysers, 4,754 +/- 1,427 vs. 6,011 +/- 856 units (p = 0.0281) and erythropoietin usage was also significantly reduced, 4,630 +/- 2,620 vs. 7,850 +/- 4,069 units (p = 0.049). There was a significant increase in hemoglobin with E15NL compared to C15NL, 115 +/- 10.4 vs. 108 +/- 13.1 (p = 0.0343). When the high-flux dialysers were compared there was a tendency towards less dialyser clotting with the EE15NL compared to F60, though this did not achieve statistical significance (p = 0.0561). We could not demonstrate any significant changes between the different dialysers with regards to PT, PTT, fibrinogen factor 12 activity, protein C, protein S and ATIII. In conclusion, we have shown that the use of vitamin-E-modified dialysers is associated with less clotting in patients with persistent clotting problems. In addition, this was associated with less heparin and erythropoietin requirements.