Pyrochlores with praseodymium as the A-site cation and zirconium, tin, cerium and manganese cations on the B-site were prepared in air and their electrical conductivities were investigated as a function of oxygen partial pressure and temperature. Pure Pr2Zr2O7+/-delta as well as samples modified on the B-site with 5% Mn or 20% Ce show conductivities, which are lower than 2 x 10(-3) S/cm at 1000 degreesC in H-2/H2O atmospheres. Electronic p-type conductivity was indicated for these materials in oxygen/nitrogen mixtures. The electrically conducting pyrochlore solid solutions Gd2TiMoO7+/-delta and Gd2Ti0.6Mo1.4O7+/-delta were synthesised and investigated in 1% H-2/3% H2O/96% N-2. No formation of a new phase by reaction with YSZ was indicated after exposure to this atmosphere at 1000 degreesC for 1000 h. Pr2Sn2O7+/-delta modified with 5% indium on the B-site exhibited a conductivity in air of 6.5 x 10(-3) S/cm at 1000 degreesC. The pure material was found to decompose in mixtures of 9% H-2/3% H2O/88% N-2. (C) 2000 Elsevier Science B,V. All rights reserved.