Potentiodynamic electrochemical impedance spectroscopy (PDEIS) uses virtual instruments to acquire, by means of a common potentiostat, multidimensional dependencies that characterise variations of dc current and frequency response in the same potential scan. Unlike classical EIS, which finds the whole equivalent circuit in stationary states, PDEIS finds, in potentiodynamic systems, only those elements of equivalent circuits that are needed to decompose the ac response in a limited range of frequencies. The decomposition of ac response into components belonging to different elements is provided by a built-in spectrum analyser, which gives dependences of equivalent circuit parameters on variable potential. The new technique develops the idea, originally suggested by D.E. Smith, of versatile characterisation of the electrochemical response in a simple computerised experiment. PDEIS solves this problem with the use of multi-frequency potentiodynamic probing based on analysis of streams of wavelets. The use of the additional variable (electrode potential) helps to disambiguate the equivalent circuit analysis. The PDEIS performance is illustrated on systems of different kind: a reversible system (ferricyanide redox transformations on glassy carbon and platinum electrodes), a system that is locally reversible but shows different responses in forward and backward scans (Bi upd on Au) and strongly irreversible variable system (initial stages of aniline electropolymerisation on gold). (C) 2004 Elsevier Ltd. All rights reserved.