Some recent excellent papers on the electrochemical treatment (ECT) of tumors provide observations for an analysis of this phenomenon from an electrochemical point of view. An attempt is made here to develop the idea that ECT is a case of electro-osmotic dewatering (EOD) of the tumor material with the consequent changes in pH, with the concomitant role of reactions at the electrodes. Some quantitative considerations explaining the role of electrochemical double layers, zeta potential and associated quantities during the electro-osmotic process are outlined. A capsule summary of the factors that may be involved in necrosis of the tumor tissue is given in which the electro-osmotic dewatering at the anode and excess water accumulation at the cathode are the paramount effects, together with the associated pH changes. © 1999 Kluwer Academic Publishers