Membrane charge affects diffusive permeability for ions. Hence, evaluation of membrane charge density is necessary to clarify diffusive permeability for ions. The objective of the present study is to measure stable and reproducible membrane potentials with hollow-fiber membranes and to evaluate the electrostatic characteristics of dialysis membrane by applying membrane potential measurement method for flat membrane to hollow-fiber membranes. Membrane charge density was calculated from data on the membrane potential. Values for membrane charge density obtained as electrostatic characteristics of AM-UP150 (regenerated cellulose), KF-15C (ethylenevinylalcohol copolymer), PAN-150SF (polyacrylonitrile), AM-BC150X (polyethylene glycol-modified regenerated cellulose), FB-150U (cellulose triacetate), APS-150E (polysulfone), FLX-15GW (polyester-polymer alloy) and BLF-10GW (diethylaminoethyl-modified regenerated cellulose) were -0.9, -0.9, -0.7, -0.5, -0.1, +0.1, +0.35 and +3.1 mol/m(3), respectively. This method allows determination of the membrane charge density of hollow-fiber dialysis membrane. (C) 2010 Elsevier B.V. All rights reserved.