In a concrete migration test the ionic species are present either in the boundary layer or in the pore solution and they flow as is indicated by the Nernst-Planck equation. This equation supposes that the flux of each ion is independent of every other one. However, due to ion-ion interactions there are ionic flelds that affect the final flux producing an additional voltage known as the membrane potential. In order to understand this phenomenon, this paper describes a theoretical and experimental investigation of I lie implications of the membrane potential on the migration of chlorides in concrete. A new electrochemical test has been carried out and its results were compared with a numerical simulation. From the results it has been proved that the voltage drop during a migration test is not linear and changes during the test. Thus the Nernst-Planck equation may be applied to the simulation of migration of any ionic species through a saturated porous medium by using the non-linear voltage to represent all the microscopic interactions in a macroscopic way. The results may be used to improve the reliability of the ASTM C1202 chloride migration test. (C) 2008 Elsevier Ltd. All rights reserved.