A process for the removal of deposits consisting essentially of the oxides of one or more transition metals from a surface, which process comprises contacting the said surface at a pH in the range of from 2.0 to 7.0 with a reagent comprising a one-electron reducing agent which is the complex formed between a low oxidation state transition metal ion and a complexing agent, for destabilizing the metal oxides deposited, thereby increasing their rate of dissolution, the complexing agent being thermally stable at the operating pH and present in order to form the necessary complex reagent and also to increase the thermodynamic solubility of the metal ions released.