In previous laboratory experiments [Mok et al., J. Geophys. Res. 107 (2002) ECV 41] we investigated the effect of high-temperature flow of a reactive fluid (i.e. water) on the transport properties of rock. Here we ran a similar experiment during which we performed transient flow measurements while monitoring the electrical potential across the rock sample. The transient flow tests were carried out at temperatures ranging from 25 to 225 degreesC. We systematically varied the sign and magnitude of the pressure pulses used. This allowed us to check the scaling properties of the recorded electrical signals and their symmetry with respect to fluid flow reversal. Together with the time dynamics of the electric signals, these scaling and symmetry properties provide very powerful tools to identify the mechanisms generating the electrical potential (e.g. electrokinetic coupling). We observed that the electrical potential exhibited sharply different phenomenological behavior depending on temperature. At low temperature (i.e. up to 70 degreesC), electro-kinetic coupling was the most likely cause of the electric signals, whereas electro-dispersion and electro-diffusion couplings predominated at temperatures higher than 100 degreesC. (C) 2003 CNR. Published by Elsevier Science Ltd. All rights reserved.