Electrochemical reductive doping and oxidative de-doping was employed to modify anatase photoelectrochemical properties in situ. Spectroelectrochemical (Raman) and surface analysis (XPS, STM) revealed that changes in surface composition are responsible for variations in the course of both dark and photoassisted charge transfer processes including sub-bandgap photoeffects. The amount of charge passed during electrochemical reduction and oxidation of the electrode served to control the doping process, the level of which was indicated by variations in the course of reactions taking place on the anatase/electrolyte interface. The electrochemical reduction and oxidation of anatase allowed the reversible alteration of the electron density and this influenced its performance as a photoelectrode. (C) 2003 Elsevier B.V. All rights reserved.