In a method for localizing at least one focal lesion in a biological tissue section, the lesion exhibiting an electrical property different from the tissue section and the electrical property in the tissue section being essentially constant, a sequence of electrical excitation signals with different frequency is applied to the tissue section, electrical response signals at a number of measurement locations at a surface of the tissue section are measured that occur thereat due to the excitation signals, frequency-independent signal parts in the response signals are determined and further-processed input values of a localization step. Modeling of the tissue section and a determination of a set of lead fields are based on the input values. The lead fields transformed. The frequency-independent signal parts are compared to the transformed lead fields in the localization step, and the location of the transformed lead fields that best reproduce the frequency-independent signal parts is output as location of the lesion.