World-wide a number of activities are concerned with the optimisation and development of cell materials and microstructures with the aim of reducing the solid oxide fuel cell (SOFC) operating temperature. Advantages for reduced operating temperatures are considered to be longer life time and reduced costs of the total system. Conventional zirconia based electrolyte cells with highly optimised electrodes have produced 500 mA/cm(2) at 700 mV and 800 degrees C. At a similar temperature and cell potential, small scale, co-fired, electrode supported thin-electrolyte cells have produced 700 mA/cm(2). For SOFC operation at temperatures below 750 degrees C the conventional 8 mol% Y2O3-ZrO2 electrolyte is replaced with either Ce0.9Gd0.1O1.95 (10GCO) or La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolytes. Up-scaled 10 x 10 cm(2) or 12 cm circular 10GCO and LSGM cells have been manufactured and the initial results of cell tests are very promising.