The exposure of blood to hemodialysis membranes results in numerous phenomena and/or complications in hemodialyzed patients, which have an influence on the quality of life (QOL) of those patients. A vitamin E-modified regenerated cellulose membrane (E-membrane) was developed to act as a scavenger for reactive oxygen species causing complications in hemodialysis patients. Neopterin (NEOP) is a metabolite derived from guanosine triphosphate with the production and release of NEOP being induced in monocytes and macrophages by cytokines such as interferon-gamma (IFN-gamma). Serum neopterin levels are shown to be a reactive marker of bioincompatibility of dialysis membranes in hemodialysis patients. The following report evaluates the usefulness of serum NEOP as a marker for the biocompatibility of the E-membrane hemodialyzer in a clinical study. In the clinical study, where extracorporeal ultrafiltration strategies with E-membranes were employed, the serum levels of NEOP were lower than those in patients using cellulose triacetate membranes (C-membranes). In the long-term evaluation of the biocompatibility of E- and C-membranes, the increase of serum neopterin levels in the C-membrane was higher than those in the E-membrane. In conclusion, the evaluation of serum neopterin levels during hemodialysis shows that the E-membrane has a good biocompatibility in hemodialyzed patients.