Measurements of the electrical conductivity of olivine buffered by magnesiow¿stite can increase by more than two orders of magnitude if as little as 2¿10-3 percent of the magnesiow¿stite is allowed to form a parallel conduction path between the electrodes. These results are used, in concert with recent petrologic studies of the distribution of iron between perovskite and magnesiow¿stite that have been synthesized from iron-bearing olivine, to show how most of the inconsistencies in diamond-anvil-cell electrical conductivity measurements of perovskite may be explained by the presence of highly conductive, through-going magnesiow¿stite layers in laser-heated samples, including those synthesized from pyroxene. Without electrical conductivity measurements on perovskite uncontaminated with secondary phases, current laboratory data can be interpreted--within constraints provided by the electrical conductivity of the mantle from geomagnetic studies--as requiring that either the conductivity of perovskite is not much different from magnesiow¿stite or that magnesiow¿stite in the lower mantle is distributed heterogeneously as an interconnected through-going phase. ¿ American Geophysical Union 1994