This paper concerns an analysis of the behavior of ionic conducting oxides brought into a chemical potential gradient, and the development of an experimental procedure for the determination of the diffusion coefficients of the most mobile species, in these materials as well as in mixed conducting compounds. The principle of the method is to place the sample between short-circuited reversible electrodes which are exposed to different chemical potentials. The ionic flux which develops then in the sample is determined from the measure of the electronic current in the external circuit. The relevant equations are given. Yttrium-doped zirconia has been used as model material. The results obtained in this work are complementary to previous data of self-diffusion and conductivity and have allowed us to obtain some information concerning the correlation factors and the structure of the defects, in this oxide.