The conductivity of the materials LaAlO3, LaGaO3, LaScO3 and LaInO3 all doped with 10% strontium on the A-site and 10% magnesium at the B-site has been measured at different temperatures and oxygen partial pressures. The doped LaGaO3 is found to be an almost pure ionic conductor with a conductivity of 95 mS/cm at 800 degrees C. The conductivity of doped LaGaO3, decreases with time due to precipitation of a secondary phase. The doped LaAlO3 and LaScO3 are mixed conductors in oxidising atmosphere. Their ionic conductivities at 800 degrees C are 1.3 and 0.5 mS/cm, respectively. The conductivities given are total conductivities. The large difference in the conductivities of the investigated materials seems to be caused partly by grain boundary resistance. (C) 2000 Elsevier Science B.V. All rights reserved.