Densi ty- functional calculations have been used to study protonic defects in stoichiometric and substituted La2Zr2O7 pyrochlore oxide. The preferred proton sites have been pinpointed in the stoichiometric material and their relative stability determined. Based on these results a continuous migration pathway that enables long-range transport is proposed. In addition, the interaction energies between protons and divalent Ba, Sr, Ca, and Mg dopants located on the La- and Zr-sites have been calculated. All interactions are found to be attractive; they are strong in the case of Ba and Mg and quite weak for Sr and Ca suggesting that samples acceptor doped with the latter two ions should show the highest proton conductivity. (c) 2007 Elsevier B.V. All rights reserved.