The impedance of the cubic perovskite BaZr0.9Y0.1O3-delta has been systematically investigated in dry acid wet atmospheres at high and low oxygen partial pressures. In the grain interior, conductivity contributions from oxygen ions, electron holes, and protons can be identified. Below 300 degrees C, proton conduction dominates and increases linearly with the frozen-in proton concentration. The proton mobility, with an activation energy of 0.44 +/- 0.01 eV is among the highest ever reported for a perovskite-type oxide proton conductor, For dry oxygen atmospheres, electron hole conduction dominates with an activation energy of similar to 0.9 eV. At temperatures <500 degrees C, the grain-boundary conductivity can be separated and increases upon incorporation of protons, The high electrical conductivity and chemical stability make acceptor-doped barium zirconate a good choice for application as a high-temperature proton conductor.