Haemodiafiltration increases convective clearances, and online haemodiafiltration (OL-HDF) was introduced to reduce costs of producing large volumes of ultrapure water. Previous reports have suggested that OL-HDF may be a cost-saving therapy by reducing recombinant human erythropoietin requirements and those for other medications. We therefore costed OL-HDF with high-flux haemodialysis.