Incoherent scatter radar measurements made in 1981 and 1982 are used to determine electrical conductivity of the nighttime E and F regions at Arecibo, Puerto Rico. The height-integrated Pedersen conductivity of the F region exceeds that of the E region by a factor of 10 on the average. We therefore conclude that, for the solar maximum conditions we have studied, the local E region has little influence on nighttime F region electrodynamcs. Simultaneous measurements of ion and neutral velocities are often inconsistent with the hypothesis that a fully developed electric polarization field is generated by dynamo action in the local F region. A better explanation of our results is obtained by including the influence of polarization fields that originate in the F region of the conjugate hemisphere.