One of the key problems of SOFCs is their slow start-up and cycling performance which is due to the thermal shock problems of zirconia electrolyte and its associated electrode and interconnect materials. Typical start-up times range from 2 to 6 h. Faster cycles can cause degradation in performance and in material integrity. The purpose of this paper is to study the transient performance of SOFCs under various (e.g. thermal and/or current load) cycling conditions, typifying start-up and shut-down as well as variable working conditions of the systems, in order to understand the degradation mechanisms. Three types of SOFC have been compared; the planar stack with metal interconnects represented by the Forschungszentrum Julich (FZJ) configuration; the Rolls Royce Fuel Cell Systems Ltd. (RRFCS) integrated planar tube; and the Adelan pure tube. The objective was to cycle in temperature from ambient to the operating condition several times to check if degradation was occurring. To obtain thermally shock resistant systems, cell dimensions had to be reduced to the millimeter scale. (C) 2007 Elsevier B.V. All rights reserved.