A symmetric solid state electrochemical cell is described, which allows simultaneous measurements of the chemical diffusion coefficients and the ionic and electronic conductivities of mixed ionic-electronic conductors as a function of composition, the latter being varied in situ by coulometric titration in the solid state. The cell contains ionic and electronic electrodes as well as ionic and electronic probes, all located at the opposite ends of the sample. The parameters are obtained from the transient voltage response of the ionic probes during polarization/depolarization experiments via the ionic or electronic electrodes. The cell is applied to alpha-Ag2Te at 300 degrees C and the results are compared with those from literature.