A series of perovskite oxides have been investigated with regard to their electronic conductivity and oxygen transport properties as well as electrode properties. The experiments were carried out on pressed samples with ceramic microelectrodes made of zirconia (20 mol% Y) or ceria (20 mol% Gd) vs. a large area Pt counter electrode and in the temperature range 600-750 degreesC. Here, we present results on the cobaltites Gd1-x SrxCoO3, Gd1-x Sr-x Co1-y Mg-y O-3, and the chromites La1-x Ca-x CrO3 and Gd1-x SrxCrO3. Gd1-x SrxCoO3 doped with 20 and 40 mol% Sr showed good oxygen ion conductivities of up to 6.0 * 10(-4) S/cm (Gd0.6Sr0.4CoO3 at 700 degreesC in air). This system also yielded a remarkable enhancement of the oxygen electrode reaction in contact with zirconia. The investigated chromites gave rather low oxygen ion conductivities, but a clear catalytic effect for the reduction of oxygen.