Electrolysis of cancer tumours (or rather of the saline fluid component of the tumour) provides a means for the electrochemical treatment (ECT) of cancerous tissues. Hydrogen evolution at the cathode causes cavitation (and hypoxia) of the tissue and chlorine evolution at the anode causes its bleaching, both thus contributing to tissue necrosis. Changes in pH caused by these electrode reactions, electroosmotic movement of water from the anode to the cathode causing dryness of the tissue in the anodic area and its oedema near the cathode area, contribute further to the necrosis. Crown Copyright (C) 2003 Published by Elsevier Ltd on behalf of the International Association for Hydrogen Energy.