The known liquid membranes (impregnated and emulsion) based on di-2-ethylhexylphosphoric acid (D2EHPA) extract nickel only out of weakly acid and neutral solutions. We have found out that direct current applied to an extraction system contributes to the complete extraction of nickel cations (0.003-0.009 M NiSO4) out of more acidic solutions (C-H2SO4 less than or equal to 0.05 M) as well. The organic membrane phase is a D2EHPA solution (20 vol%) in 1,2-dichloroethane with 5-20 vol% of tributyl phosphate (I) or 1-2 vol% n-trioctylamine (II) added. These additions increase the electrical conductivity of the system 10-20 times. This allows for the extraction of nickel cations at optimal values of current density (for I: i less than or equal to 2.1 mA/cm(2); for II: i greater than or equal to 4.9 mA/cm(2)). It is shown that the flow of nickel cations through the feed solution/organic phase interface increases with a certain increase of current density, metal content in the aqueous phase, and amount of addition of I or II in the studied concentration range. Chronopotentiograms can be used to estimate the efficiency of nickel extraction. If an electric field is applied, the transfer of nickel cations is codirected with that of hydrogen ions through the interface. Kinetic measurements of nickel cation as well as of hydrogen ion transport numbers revealed that the nickel cation extraction process was preceded by the transport of hydrogen ions through the feed solution/organic phase interface.