We have measured the electrical conductivity of (Mg0.76Fe0.24)SiO3 perovskite and of an assemblage of (Mg0.89Fe0.11)SiO3 perovskite + (Mg0.70Fe0.30)O magnesiow¿stite at pressures of 45--80 GPa and temperatures from 295 to 3600 K. The apparent activation energy for electrical conduction is 0.24 (¿0.10) eV for the perovskite and 0.20 (¿0.08) eV for the perovskite + magnesiow¿stite assemblage. Comparing our present results with those derived previously for Fe-poor samples, we find that the electrical conductivities of both the silicate perovskite and the perovskite + magnesiow¿stite assemblage depend strongly on iron content. Thus the electrical conductivity distribution inside the Earth could provide an important constraint in modeling the composition of the lower mantle. ¿ American Geophysical Union 1991