Abstract: Diagnostic method and sensor device for detecting the location and/or character of lesions in body tissues. Electrodes of different substances are put onto or into a tissue being tested, the electrodes are nearly short-circuited over a measuring device, and the current flowing through the terminals of the electrodes is measured. The measured value of the current is then compared with a control value measured in the same way on a piece of sound tissue. One embodiment of a sensor device that can be applied for the performance of the method comprises a pair of electrodes, made of different materials so as to have different contact potentials, the electrodes being coupled to an electric measuring instrument, e.g. an ammeter, one of the electrodes being a metal tube such as a medical syringe, whereas the other electrode is enveloped by an insulating material and fixed inside the metal tube.