Investigations of perovskite-type BaCeO3 and SrCeO3 with various dopants (Y, Gd, Nd, and Ni) indicate that their microstructures and electrical properties are strongly influenced by the type and amount of dopants. Grain growth and densification of sintered samples are influenced by dopant level and A:B site nonstoichiometry. The conductivity of BaCe1-xYxO3-delta increases with the yttrium content in hydrogen and wet Ar, and exhibits a maximum in oxygen at an yttrium content of 10 to 20%. BaCe0.8Y0.2O3-delta, has the highest conductivity in a hydrogen atmosphere : similar to 1.54 x 10(-2) Omega(-1) cm(-1) at 600 degrees C, and similar to 4.16 x 10(-2) Omega(-1) cm(-1) at 800 degrees C. The effect of BaO excess depends on the concentration of dopant. Compared with BaCe0.95Y0.05O3-delta, doped BaCeO3 with BaO excess (BaO.0.90CeO(2).0.025Y(2)O(3)) has a higher total conductivity in all atmospheres studied (O-2, H-2, and wet Ar), whereas the conductivity of BaCeO3 with excess BaO (BaO.0.85CeO(2).0.05Y(2)O(3)) is lower than that of BaCe0.9Y0.1O3-delta. BaCeO3 based materials have higher conductivities than those of SrCeO3 based materials, whereas SrCeO3 based materials show higher proton transference numbers.