A straightforward theoretical description of the time-dependent response of ion-selective membrane electrodes to multiple sample changes is presented. The derivation makes use of an approximation for the ion fluxes in the membrane, and of the superposition of partial fluxes induced by the step-changes. The general theory allows for any number of samples and ions. It is applied for the analysis of memory effects that reflect the influence of preceding samples on subsequent measurements. Various phenomena are discussed, including super-, near-, or sub-Nernstian responses, shifts of apparent reference potentials. and potential dips with domains of reversed slopes. The theoretical results agree well with virtual experiments based on computer simulation. (C) 2009 Elsevier B.V. All rights reserved.