In the preoperative investigation of partial epilepsies, electrical characteristics of the so-called epileptogenic area are of critical interest to localize this area. We have always emphasized that the analysis of ictal events themselves, is more valuable than that of inter-ictal anomalis. One reason for this emphasis has been the absence of a reliable method to evaluate the relationship between the topography of ictal and interictal events. An technique for imaging an intracerebral potential field is reported. It allows to analyse the spatio-temporal distribution of interictal events recorded during the SEEG exploration. This technique applied to an illustrative patient shows that the temporo-spatial distribution of interictal spikes is related to that of the ictal discharge itself. A new hypothesis concerning the build up of an epileptogenic area in man is presented.