In vitro data have shown an increased cytotoxic drug uptake into electropermeabilized cells in suspension, leading to a marked cytotoxicity increase (1). Preclinical experiments were required to demonstrate the in vivo applicability of these observations. Obviously, the most convenient laboratory animal model to test new antitumor treatments is the mouse. Indeed, there exist many tumors of different histological types which can be transplanted in mice, either in immunocompetent mice in the case of syngeneic tumors or in immunodepressed mice in the case of allogeneic or xenogeneic tumors. From a practical point of view, mice have the advantage to be rather cheap and to allow a large number of experiments. Moreover, murine tumors are generally easy to transplant, grow rapidly, and can be conveniently followed for their evolution, at least in the case of subcutaneous tumors. Finally, murine subcutaneous tumors are well adapted to test the antitumor effects of electrochemotherapy since they allow the use of a rather simple material to conveniently apply transcutaneous permeabilizing electric pulses.