The purpose of this work is to study diffusion potentials (i.e., liquid junction potentials) established between two static or flowing solutions in microsystems. One of the motivations of investigating the diffusion potential distribution is to be able to establish a potential gradient in a cell without introducing electrodes and using a potentiostat. By using finite element simulations, different geometries (i.e., microhole, Y-channel mixing and microtube injection) have been studied numerically. The calculations have allowed systematic studies of the influence of concentration ratio, flow rate and detector position. It is shown that the diffusion potential can be a useful way to quantify the degree of mixing or filling of solutions in microsystems. The theoretical part has been corroborated by experimental measurements of potential differences across a parallel flow channel, taking into account the diffusion potential and differences in the electrode potentials. It is apparent that the theoretical model gives a good fit to the experimental results. (C) 2003 Elsevier Science B.V. All rights reserved.