In the present study kindling was induced in rats by repeated intraperitoneal injection of pentylenetetrazol (PTZ) once every 48 h. The resulting seizure stages were registered after each PTZ application. The development of PTZ-induced kindling and the time course of possible potentiation effects in the dentate gyrus were examined. The efficacy of perforant pathway transmission to the granule cells was tested in every second kindling session by measuring the monosynaptic evoked field potentials recorded in the dentate gyrus following single test stimuli of the perforant pathway at different times after PTZ injection in freely moving animals. The data suggest that establishment of a PTZ kindling is associated with the development of long-lasting potentiation of the field potentials. After completion of kindling it was demonstrated that kindled rats also show a diminished learning performance. The relationship between the development of potentiation phenomena in hippocampal substructures and learning impairment is discussed.