A dc electric field experiment on the Air Force satellite S3-2 has occasionally detected intense localized electric fields near the ionosphere projection of the plasmapause. These poleward directed electric fields were observed in the pre-midnight local time sector, seem to be related to substorm activity, and typically exceeded 100mV/m. In one case the field was 280mV/m corresponding to a drift velocity of 9.8 km/s at an altitude of 1463 km and a potential drop of 25 kilovolts. A possible source lies in the interaction between hot plasma freshly injected near magnetic midnight and the cold plasmaspheric particles. Since the potential drop is the order of the mean ring current energy, this structure may have important consequences for the understanding of magnetospheric flow patterns under disturbed conditions. ¿ 1977 American Geophysical Union