A measurement set-up is presented containing a multichannel frequency response analyser system that allows the measurements of impedance spectra of single cells in a fuel cell stack simultaneously. As a proof of reliability, the sum of the impedances of the single cells is compared to the measured impedance of the whole stack. A good correlation was found. The absolute deviation is less than 2.5%. A measurement of the stack during low load operation is presented. Differences in the individual cell voltages are investigated. A flooding event in a single cell is observed by means of the impedance measurement minutes before the polarisation shows a voltage drop. (c) 2005 Elsevier B.V. All rights reserved.