The influence of humidity on the conduction of indium doped calcium zirconate is investigated using electrochemical hydrogen concentration cells. The resulting e.m.f. values measured in dry and humidified argon-hydrogen gas mixtures were found to be linear as a function of the logarithm of the hydrogen gradient but with a slope of around 70% of the expected Nernst slope in the dry mixtures. The obtained curves are discussed in terms of mixed hydrogen and oxygen conduction. In addition, electronic conduction at very low oxygen partial pressures was introduced in order to explain all the experimental observations.