Previously published data on the conductivity changes induced in rutile (TiO2) by an applied field are reinterpreted in the light of new information on the behavior of donor impurities in this crystal. It is suggested that the large increase in conductivity which is usually observed is electronic in nature, and is due to an increase in H+interstitial concentration. The H is introduced at the anode, probably by electrolysis of H2O, migrates through the crystal under the influence of the applied field, then is neutralized at the cathode and escapes from the crystal. Enhanced conductivity results when migration of H+near the cathode is inhibited by Ti4+interstitials, thus increasing H+concentration in the bulk. Other possible mechanisms are considered.