We have investigated certain aspects of the dielectric properties of anodic oxide films on tantalum in connection with Dignam's theory that a special current-driven polarization process is responsible for the transients shown by the ionic current on changing the electric field in the oxide. In his experiments, which were claimed to prove this theory, films were first held at potentials giving fields too low to produce significant ionic current. When voltage pulses were applied large enough to produce fields giving ionic current, extra current was observed to flow for a short time. This was taken as due to the decay of the dielectric polarization built up due to the ionic current, and partial numerical agreement with the model was found. In the present experiments the discharge current flowing after longer periods of voltage application or of ionic current flow was investigated with the aim of finding if more polarization was indeed produced by ionic current flow. The current was not found to be larger after discharge from fields giving ionic current, as required by Dignam's model. It is argued that structural changes in the glassy oxide are responsible for the transients. (c) 2006 The Electrochemical Society. [DOI: 10.1149/1.2405869] All rights reserved.