This paper reports oxide ion conductivity measurements on pyrozirconates of neodymium and gadolinium in which the rare earth elements were partially substituted by strontium, and zirconium partially substituted by aluminium. 5-10 atom% Sr and very little Al were found to enter the pyrochlore lattice, ac impedance measurements have shown an enhancement of conductivity as a result of the incorporation of small amounts of Sr in both the pyrochlores. In the Gd2Zr2O7 system, this could be traced to an improvement of the grain interior conductivity, by resolving the grain interior and grain boundary contributions to the total conductivity. Such a separation of the bulk and grain boundary conductivities could not be achieved in the Nd2Zr2O7-based compositions. The observed variations in conductivity are explained in terms of the pyrochlore crystal chemistry. © 1995.