 Today, an increasing number of patients with chronic renal failure CRF is treated with on-line hemodiafiltration HDF. This practice is based on the assumption that the high incidence of cardiovascular CV disease, as observed in patients with CRF, is at least partially related to the retention of uremic toxins in the middle and large-middle molecular MM range. As HDF lowers these molecules more effectively than HD, it has been suggested that this treatment improves CV outcome, if compared to standard HD. 