Two methods for the estimation of the current bypass in solid state electrochemistry are presented. The current bypass was estimated from the current-voltage curves of a tubular cell with one bipolar element and from the current-voltage curves of a monolith with several bipolar elements. A current bypass of 11.5% was found in the tubular cell and a current bypass of 34% in the monolithic configuration, both at high cell voltages. The current bypass in the tubular cell was found to be almost independent on the applied current between 500 and 1000 muA. The current bypass did not show an important influence on the electrochemical promotion. A much more important influence was found due to the bipolar polarisation of the catalyst. The nonuniform distribution of the work function led to a smaller increase of the ethylene conversion during the bipolar polarisation than during the direct anodic polarisation. (C) 2000 Elsevier Science Ltd. All lights reserved.