The spinel ceramic material nickel germanate,Ni2GeO4,has been found to exhibit a humidity-dependent impedance. A change in the magnitude of the impedance at 100 Hz, from108&OHgr; at 20&percent;RHto104&OHgr; at 98&percent;RH,at 298 K, is typical. The effect of frequency on the complex impedance has been investigated over the frequency range 10 mHz–10 MHz, using the technique of impedance spectroscopy. The observed impedance spectra show two regions, indicative of an ionic-charge transport process and a charge transfer to the electrodes, suggesting that at high levels of humidity conduction is essentially electrochemical. ©1998 American Institute of Physics.